Category: CBSE

Class 6 Maths Notes students can refer to the Playing With Numbers Class 6 Notes Maths Chapter 3 https://www.cbselabs.com/playing-with-numbers-class-6-notes/ Pdf here. They can also access the CBSE Class 6 Playing With Numbers Chapter 3 Notes while gearing up for their Board exams.

CBSE Class 6 Maths Notes Chapter 3 Playing With Numbers

Playing With Numbers Class 6 Notes Chapter 3

A number which divides a given number are 1,2,3 and 6; exact divisors or factors of 15 are 1, exactly is called an exact divisor or factor of that 3, 5 and 15. number.
For example exact divisors or factors of 6 are 1, 2, 3 and 6; exact divisors or factors of 15 are 1, 3, 5 and 15.

Factors and Multiples
A factor of a number is an exact divisor of that number. In turn, a number is a multiple of each of its factors. Some interesting facts about factors and multiples are as follows:

• 1 is a factor of every number.
• Every number is a factor of itself.
• Every factor of a number is an exact divisor of that number.
• Every factor of a number is less than or equal to that number.
• The factors of a given number are finite in number.
• Every multiple of a number is greater than or equal to that number.
• The multiples of a given number are infinite in number.
• Every number is a multiple of itself.

Class 6 Maths Chapter 3 Notes

Perfect number: If the sum of all the factors of a number is equal to twice the number, then that number is called a perfect number.
For example: 28 is a perfect number because all the factors of 28 are 1,2,4,7,14 and 28 whose sum = 1 + 2 + 4 + 7 + 14 + 28 = 56 = 2 × 28, whereas 10 is not a perfect number because all the factors of 10 are 1, 2, 5 and 10 whose sum = 1 + 2 + 5 + 10 = 18 ≠ 2 × 10.

Prime and Composite Numbers
Prime numbers: The numbers having exactly two factors 1 and the number itself are called prime numbers.
For example, 2, 3, 5, 7, 11, etc. are prime numbers.

Composite numbers: The numbers having more than two factors are called composite numbers.
For example 4, 6, 8, 9, 10. etc. are composite numbers.
Note: The number 1 is neither prime nor composite.

Even number: A number which is a multiple of 2 is called an even number.
For example: 2, 4, 6, 8, 10,….

Playing With Numbers Class 6 Notes Pdf Chapter 3

Odd number: A number which is not a multiple of 2 is called an odd number.
For example: 1, 3, 5, 7, 9,…

A number with 0, 2, 4, 6, 8 at the unit’s place is an even number.
So, 250, 2732, 29354, 34596 are even numbers.
Obviously, the numbers 257, 3249, 7321 are odd numbers.

2 is the smallest prime number which is even.

Every prime number except 2 is odd.

Tests for Divisibility of Numbers
A number is divisible by 10 if it has 0 in its units place.

A number is divisible by 5 if it has either 0 or 5 in its units place.

A number is divisible by 2 if it has any of the digits 0, 2, 4, 6 or 8 in its units place.

A number is divisible by 3 if the sum of its digits is a multiple of 3.

A number is divisible by 6 if it is divisible by 2 and 3 both.

A number with 3 or more digits is divisible by 4 if the number formed by its last two digits (i.e., units and tens) is divisible by 4.

A number with 4 or more digits is divisible by 8 if the number formed by its last three digits is divisible by 8.

A number is divisible by 9 if the sum of all the digits of the number is divisible by 9.

A number is divisible by 11 if the difference between the sum of the digits at odd places (from the right) and the sum of the digits at even places (from the right) of the number is either 0 or divisible by 11.

Playing With Numbers Notes Chapter 3 Class 6

Common Factors and Common Multiples
The factors which are the factors of each of the given numbers are called their common factors.
For example:
Factors of 20 are 1, 2, 4, 5, 10 and 20.
Factors of 48 are 1, 2, 3, 4, 6, 8, 12, 16, 24 and 48.
Clearly, the factors common to the factors of 20 and 48 are 1, 2, 4. These are called common factors of 20 and 48.
Note: Common factors are finite in number.

Co-prime numbers: Two numbers are said to be co-prime if they have 1 as the only common factor.
For example, 8 and 25 are co-prime numbers whereas 4 and 10 are not co-prime numbers.

The multiples which are the multiples of each of the given numbers are called their common multiples.
For example:
Multiples of 2 are 2, 4, 6, 8, 10, 12,
Multiples of 3 are 3, 6, 9, 12, 15, 18,
Clearly, the multiples common to the multiples of 2 and 3 are 6, 12, These are called common multiples of 2 and 3.
Note: Common multiples are infinite in number.

Some More Divisibility Rules
If a number is divisible by another number, then it is also divisible by each of the factors of that number.
For example, 40 is divisible by 20.
Factors of 20 are 1, 2, 4, 5, 10 and 20.
Clearly, 40 is divisible by each of these factors

If a number is divisible by two co-prime numbers, then it is also divisible by their product.
For example, 40 is divisible by 4 and 5. 4 and 5 are co-prime.
Their product is 4 × 5 = 20.
Clearly, 40 is divisible by 20.

If two given numbers are divisible by a number, then their sum is also divisible by that number.
For example, The numbers 10 and 25 are divisible by a number 5.
Their sum is 10 + 25 = 35.
Clearly, 35 is divisible by 5.

If two given numbers are divisible by a number, then their difference is also divisible by that number.
For example, The numbers 10 and 25 are divisible by a number 5.
Their difference is 25 – 10 = 15.
Clearly, 15 is divisible by 5.

Class 6 Maths Chapter 3 Notes Pdf

Prime Factorisation
Factorisation: A number when expressed as a product of its factors is said to be factorised.
For example: 12 = 3 × 4. We say that 12 has been factorised. This is one of the several factorisations of 12.
The others are:
12 = 2 × 6
12 = 3 × 4
12 = 1 × 12.

Ncert Class 6 Maths Chapter 3 Notes

Prime Factorisation: It is the ultimate factorisation of a given number. Moreover, it is unique (exactly one).
For example: While factorising 12, we ultimately reach the unique factorisation 2 × 2 × 3. In this factorisation, the only factors 2 and 3 are prime numbers. Such a factorisation of a number is called prime factorisation of that number. Thus, 2 × 2 × 3 is the only prime factorisation of 12.

Prime Factorisation Property
or
The Fundamental Theorem of Arithmetic
Every number greater than 1 has exactly one prime factorisation.
or
The prime factorisation of a number (>1) is unique.
0r
There exists only one prime factorisation of a number.

Notes On Playing With Numbers Class 6 Chapter 3

Factor tree: When we go on factorizing a number till we reach its ultimate factorisation and write the process as follows, we get the shape of a tree called Factor tree.
For example: Let us factorize 90. Let us see below:

Thus. 90 = 2 × 3 × 3 × 5.

Factors And Multiples Class 6 Notes Chapter 3

Highest Common Factor (HCF)
The Highest Common Factor (HCF) of two or more given numbers is the highest (or greatest) of their common factors. It is also known as the Greatest Common Divisor (GCD).
For example: Consider two numbers 12 and 20. Factors of 12 are 1, 2, 3, 4, 6 and 12. Factors of 20 are 1, 2, 4, 5, 10 and 20. The common factors of 12 and 20 are 1, 2 and 4. The highest of these is 4. So, 4 is the HGF of 12 and 20.

Lowest Common Multiple (LCM)
The Lowest Common Multiple (LCM) of two or more given numbers is the lowest (or smallest or least) of their common multiples.
For example: Consider two numbers 12 and 20.
Multiples of 12 are 12, 24, 36, 48, 60, 72, 84, 96, 108, 120, …
Multiples of 20 are 20, 40, 60, 80, 100, 120, ……..
The common multiples of 12 and 20 are 60, 120,…
The lowest of these is 60.
So, 60 is the LCM of 12 and 20.

Some Problems on HCF and LCM
In our everyday life, we are confronted with many situations in which we find it desirable to use the concepts of HCF and LCM.

Class 12 Chemistry Notes students can refer to the Chemical Kinetics Class 12 Notes Chemistry Chapter 4 https://www.cbselabs.com/chemical-kinetics-cbse-notes-class-12-chemistry/ Pdf here. They can also access the CBSE Class 12 Chemical Kinetics Chapter 4 Notes while gearing up for their Board exams.

Chemical Kinetics Class 12 Notes Chemistry Chapter 4

Chemical Kinetics Class 12 Notes Chapter 4

1. Chemical kinetics is the branch of chemistry which deals with the study of rates (or fastness) of chemical reactions, the factors affecting it and the mechanism by which the reactions proceed.
2. Rate of reaction is the change in concentration of reactants or products per unit time.
For a general reaction, A+B –> C
The rate of reaction

The negative sign indicates that the concentration is decreasing with time.
Unit for reaction rate is mol L^-1s^-1.
3. The rate of reaction is not a constant quantity (except for zero order reactions). It decreases as the reaction proceeds in the forward direction.
4. A rate law expresses a mathematical relationship between the reaction rate and the molar concentration of one or more reactants.

Where m and n are determined experimentally and represent the order of reaction with respect to A and B respectively, m + n represents the overall order of reaction.

Chemical Kinetics Notes Chapter 4 Class 12

5. Rate constant is the rate of reaction when the concentration of each of reacting species is unity. It is represented by ‘k’ It is also called specific reaction rate or velocity constant of reaction.
6. Order of reaction is defined as the sum of the exponents to which the concentration terms are raised in the rate equation (or rate law) of the reaction. It can be fraction, zero or any whole number.
7. Modularity of reaction is defined as the number of reacting particles (atoms or molecules or any other species), which collides simultaneously to bring about the chemical change.
It is a theoretical concept. Its value is always a whole number. It is never more than three. It cannot be zero.
8. First order reaction: A reaction is said to be first order if its reaction rate is determined by the variation of one concentration term only.
9. The integrated rate equation expresses the concentration of reactants as a function of time.
10. The integrated rate equation for a first order reaction is given as

11. Second order reaction: The reaction in which sum of powers of concentration terms in rate law equation is two.

Class 12 Chemistry Chapter 4 Notes

12. Zero order reaction: Those reactions in which rate of reaction does not change with concentration of the reactants.
Rate law for such a reaction is expressed as. Rate = k [A]°[B]°
13. Half life period: It is the time required for the initial concentration of the reactant to be reduced to half its value.

Class 12 Chemical Kinetics Notes

14. It has been found that for a chemical reaction with rise in temperature by 10 °C, the rate constant gets nearly doubled.
15. The temperature coefficient of a reaction is the ratio of the rate constants of the reaction at two temperatures differing from one another by 10°C. The two temperatures usually taken are 35 °C and 25 °C.
16. The variation of rate constants with temperature can be represented by the Arrhenius equation,
K=Ae^-Ea/Rt
 where A is a constant known as frequency factor, and Ea is-called the energy of activation.
From the above equation, the rate constants at two different temperatures are related as

Chapter 4 Chemistry Class 12 Notes

17. There are two important theories of reaction rates:
(i) Collision theory and,
(ii) Transition state theory.

Class 12 Chemistry Notes students can refer to the Biomolecules Class 12 Notes Chemistry Chapter 14 https://www.cbselabs.com/biomolecules-cbse-notes-for-class-12-chemistry/ Pdf here. They can also access the CBSE Class 12 Biomolecules Chapter 14 Notes while gearing up for their Board exams.

Biomolecules Class 12 Notes Chemistry Chapter 14

Biomolecules Class 12 Notes Chapter 14

1. Carbohydrates is a class of compounds that include polyhydric aldehydes and ketones and large number of other polymeric molecules that yield these on hydrolysis, e.g., sugars, glycogen, cellulose, starch, etc.
2. Depending upon their behaviour on hydrolysis, carbohydrates are further divided into three types: Monosaccharides (e.g., glucose, fructose etc.), disaccharides (e.g., sucrose, maltose etc.) and polysaccharides (e.g., starch, cellulose, etc.)
3. Another classification of carbohydrates is as sugars and non sugars. Sugars are sweet in taste, crystalline, soluble in water, mainly include mono and oligosaccharides. Non Sugars are tasteless, amorphous, water insoluble and mainly include polysaccharides.
4. Carbohydrates can also be classified as reducing and non reducing sugars. Reducing sugars respond to Tollens’ and Fehling solution test. All monosaccharides, aldoses and ketoses,fall in this category. Some other oligosaccharides also may be reducing. All polysaccharides are non reducing (starch, cellulose, glycogen etc). Sucrose is a disaccharide and non reducing sugar.

Biomolecules Notes Class 12 Chapter 14

5. The molecular formula of glucose is C₆H₁₂O₆. It is prepared by boiling sucrose with dil HCl or dil H₂SO₄ in alcoholic solution or by the hydrolysis of starch with dil H₂SO₄ at 393 K under pressure.
6.The Fisher projection for D-and L-glucose are shown below:

7. A pair of stereoisomeric ring forms of any sugar differing in configuration only at carbon 1 (the anomeric carbon) are called anomers.
8. The spontaneous change that takes place in specific rotation of an optically active sugar when dissolved in water is known as mutarotation.
9. The cyclic structure of glucose was proposed by R. D. Haworth. The six-membered cyclic structure of glucose is called as pyranose structure (α or β).

Biomolecules Class 12 Chemistry Notes Chapter 14

10. The hydrolysis of sucrose brings about a change in the sign of rotation, from dextro (+) to laevo (-). Such a change is known as inversion of sugar.
11. Starch/Amylum (C₆H₁₀O₅)_n is a polymer of D-glucose and consists of two components amylose and amylopectin. Natural starch consists of approximately 15 – 20% of amylose and 80 -85% of amylopectin.
12. Cellulose (C₆H₁₀O₅)_n is a linear polymer of β-D-glucose in which the β-D- glucose units are joined by β-D-glucosidic linkage.
13. Proteins are the most abundant biomolecules of the living system. They are required for growth and maintenance of body. All proteins are polymers of α-amino acids.
14. The amino acidsare the compounds containing at least one amino (-NH₂) and one carboxyl
(-COOH)ftactional group. The amino acids are classified as α , β , γ, δ and so on depending upon the position of the two functional groups in the alkyl chain.

Biomolecules Notes Chapter 14 Class 12

15. There are 20 different amino acids, each with a different – R group, commonly found, in the proteins of living things. The human body can  synthesis 10 out of the 20 amino acids found in
the proteins. These are called non-essential amino acids, e.g., glycine, alanine, aspartic acid, glutamic acid, etc.
16. Certain amino acids are required for proper health and growth in human beings. But the human body is unable to synthesize them. These must  be supplied to body through food and are called essential amino acids, e.g., valine, leucine, phenylalanine, etc.
17. Denaturation refers to the loss of a biological activity of a protein brought about by changes in its secondary and tertiary structure due to heat, pH change, presence of salts, etc.
18. Enzymes are naturally occurring simple or conjugated proteins that catalyse biological reactions.
19. Vitamins are substances necessary to maintain normal health, growth and nutrition. They cannot
be synthesized by organisms mid thus have to be supplied in the diet. Vitamins A, D, E and K are fat soluble whereas vitamins B and C are water soluble.

Class 12 Biomolecules Notes Chapter 14

20. Nucleic acids are polymers of complex repeating units called nucleotides. There are two types of nucleic acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
21. Nucleic acids play two important functions replication and protein synthesis.
22. A nucleotide consists of three parts:
(a) A five carbon atom sugar unit, which is either ribose and deoxyribose.
(b) A nitrogen containing heterocyclic base, and
(c) A phosphate group.

Notes Of Biomolecules Class 12 Chemistry Chapter 14

23. The nitrogen containing bases in nucleotides belong to the following two classes:
(i) Purines: The bases derived from purines are adenine (A) and guanine (G).
(ii) Pyrimidines: The bases derived from pyrimidines are cytosine (C), thymine (T) and uracil (U).
24. A mutation is a chemical change in DNA molecule that could lead to synthesis of proteins with an altered amino acid sequence. The changes in a DNA molecule can happen spontaneously or may be caused by radiation, chemical agents or viruses.

Class 12 Chemistry Notes students can refer to the Amines Class 12 Notes Chemistry Chapter 13 https://www.cbselabs.com/amines-cbse-notes-class-12-chemistry/ Pdf here. They can also access the CBSE Class 12 Amines Chapter 13 Notes while gearing up for their Board exams.

Amines Class 12 Notes Chemistry Chapter 13

Amines Class 12 Notes Chapter 13

1. Amines are the derivatives of ammonia in which one or more hydrogen atoms have been replaced by alkyl groups.
2. Amines are classified as primary, secondary, or tertiary according as one, two or three hydrogen
atoms in the ammonia molecule have been substituted by alkyl groups.
3. Preparation of amines:
(i) By reduction of nitro compounds.
(ii) An alkyl or benzyl halide on reaction with an ethanolic solution of ammonia undergoes nucleophilic substitution reaction in which the halogen atom is replaced by an amino (-NH₂) group.
(iii) By reduction of nitriles.
(iv) By reduction of amides.
(v) By Ghbriel phthalimide synthesis: For primary alkyl amines only, not for aromatic amines.
(vi) By Hoffmann bromide degradation reaction:

Amines Notes Class 12 Chapter 13

4. All the three classes of aliphatic amines (1°, 2°and 3°) form H-bonds with water. As a result, lower aliphatic amines are soluble in water.
5. Some important reactions of amines
(i) Amines are basic in nature they react with acid to form salt.

(ii) Aliphatic and aromatic primary and secondary amines react with acid chlorides, anhydrides and esters by nucleophilic substitution reaction. This reaction is known as acylation.
(iii) Aliphatic and aromatic primary amines on heating with chloroform and ethanolic potassium hydroxide form isocyanides or carbylamines which are foul smelling substances. Secondary and tertiary amines
do not show this reaction. This reaction is known as carbylamine reaction or isocyanide test and is used as a test for primary amines.
(iv) CH₆H₅SO₂Cl is also called Hinsberg’s reagent and reacts with primary and secondary amines to form sulphonamides. Tertiary amines do not react with benzene sulphonyl chloride.

Amines Notes Chapter 13 Class 12

6. Diazonium salt have the general formula RN₂⁺ X^–, where R stands for an aryl group and X^– ion maybe Cl”, Br, HSO₂^–, BF₄^–, etc.
7. Primary aliphatic amines form highly unstable alkyl diazonium salts which decomposes to give alcohols with the evolution of N₂. Primary aromatic amines form arene diazonium salts which are stable for a short time in solution at low temperature (273 -278 K).
8. Arenediazonium ion is resonance stabilized.
9. Benzene diazonium chloride is prepared by the reaction of aniline with nitrous acid at 273 – 278 K. This conversion of primary aromatic amines into diazonium salt is known as diazotisation.

Class 12 Amines Notes Chapter 13

10. Chemical properties:
(i) Diazonium group being a very good leaving group, is substituted by other groups such as Cl^–, Br^–, I^–, CN^– and OH^–.
(ii) The Cl^–, Br^– and CN^– nucleophiles can easily . be introduced in the benzene ring in the presence of Cu (I) ion. This reaction is called Sandmeyer reaction.
(iii) The reaction in which chlorine or bromine is introduced in the benzene ring by treating the diazonium salt solution with corresponding halogen acid in the presence of copper powder is called Gatterman reaction.
11. Importance of diazonium salts: They are very good intermediates for the introduction of -F, -Cl, -Br, -I, -CN, -OH, -NO₂ groups into the aromatic ring.

Class 12 Chemistry Notes students can refer to the Aldehydes, Ketones and Carboxylic Acids Class 12 Notes Chemistry Chapter 12 https://www.cbselabs.com/aldehydes-ketones-carboxylic-acids-cbse-notes-class-12-chemistry/ Pdf here. They can also access the CBSE Class 12 Aldehydes, Ketones and Carboxylic Acids Chapter 12 Notes while gearing up for their Board exams.

Aldehydes, Ketones and Carboxylic Acids Class 12 Notes Chemistry Chapter 12

Aldehyde Ketone And Carboxylic Acid Notes Chapter 12 Class 12

1. The classes of organic compounds containing carbonyl group (CO) as the functional group are aldehydes, ketones, carboxylic acids and their derivates. These are collectively called carbonyl compounds.
2. Nature of carbonyl group: Oxygen atom in carbonyl group is far more electronegative than carbon atom. As a result, the oxygen atom tends to attract the electron cloud of the π-bond towards itself, i. e., the π-electron cloud of >c = O is unsymmetrical.
Hence carbonyl carbon acquires positive charge and carbonyl oxygen carries negative charge. Thus, the carbonyl group is polar in nature.
3. Methods of preparation of Aldehydes and Ketones:
(a) By controlled oxidation of primary and secondary alcohol, aldehydes and ketones are produced.
(b) By dehydrogenation of alcohols : Primary alcohols on dehydrogenation produce aldehydes while secondary alcohols produce ketones.

Aldehydes Ketones And Carboxylic Acids Notes Chapter 12

4. Preparation of Aldehydes:
(a) Acyl chloride (acid chloride) is hydrogenated using, palladium on barium sulphate which is partially poisoned by the addition of S or quinoline. This reaction is called Rosenmund reduction. This method is used to prepare aldehydes.
(b) N itriles are reduced to corresponding imine with stannous chloride in the presence of hydrochloric acid, which on hydrolysis give corresponding aldehyde. This reaction is called Stephen’s reduction.
Chromyl chloride (CrO₂ClO₂) oxidises methyl group of toluene to a chromium complex, which on hydrolysis gives corresponding benzaldehyde. This reaction is called Etard reaction.
(d) When benzene or its derivatives is treated with CO and HCl in the presence of anhydrous AlCl₃ or CuCl, it gives benzaldehyde or substituted benzaldehyde. This reaction is called Gatterman-Koch reaction.

Class 12 Chemistry Chapter 12 Notes

5. Preparation of Ketones:
(a) Treatment of acyl chlorides with dialkyl cadmium, prepared by the reaction of cadmium chloride with Grignard reagent, gives ketones.
(b) From nitriles:

When benzene or substituted benzene is treated with acid chloride in the presence of anhydrous A1C13, the corresponding ketone is formed. This reaction is known as Friedel-craft’s acylation reaction.
Properties of aldehyde and ketones
(a) Aldehydes are much more reactive than ketones in nucleophilic addition reactions.
(b) Nucleophilic addition reactions: Aldehydes and ketones undergo nucleophilic addition reactions onto the carbonyl group with a number of nucleophiles such as HCN, NaHSO₃, alcohols, ammonia derivatives and Grignard reagents.
(c) Reduction to alcohols: Aldehydes and ketones on reduction gives primary and secondary alcohols respectively.
(d) The carbonyl group of aldehydes and ketones is reduced to CH₂ group on treatment with zinc amalgam and concentrated hydrochloric acid (Chemmenson reduction) or with hydrazine followed by heating with NaOH or KOH in high boiling solvent such as ethylene glycol (Wolff-Kishner reduction).
(e) Tollen’s reagent (ammonical silver nitrate) oxidises aldehyde and the silver ions are reduced to silver which appear as a bright silver mirror on the side of the test tube ketones do not give this test.
(f) Aldehydes reduce Fehling’s solution to form a red precipitate of cuprous oxide. Fehling’s solution is obtained by mixing a solution of copper sulphate and a solution of sodium hydroxide and sodium potassium tartrate. Ketones do not reduce Fehling’s solution..Hence no precipitate is formed.
(g) Aldehydes and ketones having atleast one α-hydrogen atom undergoes a condensation reaction when warmed with dilute alkali to form β -hydroxy aldehydes or β-hydroxy ketones respectively. The reaction is known as aldol condensation.
(h) The condensation of a mixture of two different aldehydes or/and ketones each having an a-hydrogen atom, in presence of dilute alkali gives a mixture of four products. The reaction is known as cross aldol condensation.

Aldehydes Ketones And Carboxylic Acids Class 12 Notes

6. Cannizzaro reaction: Aldehydes which do not have an a-hydrogen atom, undergo self-oxidation and reduction (disproportionation) reaction on treatment with concentrated alkali. In this reaction, one molecule of the aldehyde is reduced to alcohol white another is oxidised to carboxylic acid salt.
7. Electrophilic substitution reaction: It takes place at the ring in which the carbonyl group acts as a deactivating and meta-directing group.
8. Methods of preparation of carboxylic acids:
(a) From oxidation of primary alcohols and aldehydes.
(b) Aromatic carboxylic acids can be obtained by side chain oxidation of alkyl benzenes.
(c) From hydrolysis of nitriles and amides:
(d) From reaction of Grignard reagents with carbon dioxide:
9. Aliphatic carboxylic acids having up to four carbon atoms are miscible in water due to the formation of hydrogen bonds with water.

Notes Of Aldehyde Ketone And Carboxylic Acid Class 12 Chapter 12

10. The solubility decreases as the number of carbon atoms increases.
(i) The electron withdrawing group (Cl, NO₂, CN, etc.) stabilises the carboxylate anion by dispersing the negative charge of the carboxylate anion, RCOO^–, and thus increases the acidic strength.
(ii) The presence of electron donating substituent such as alkyl group intensifies the negative charge on the RCOO^– anion and destabilises it thereby making the carboxylic acid less acidic.
(iii) Carboxylic acids having an α-hydrogen are halogenated at the α-position on treatment with chlorine or bromine is the presence of small amount of red phosphorus to give α- chloro or  α – bromo carboxylic acids. This reaction is known as Hell-Volhard Zelinsky Reaction.