NEET ChemistryUpdated 19 Oct 2026

Some Basic Concepts of Chemistry: NEET PYQs and weightage

Some Basic Concepts of Chemistry carries 3.4 of 100 Chemistry marks in NEET by past-paper share: 24 of the 707 tagged NEET Chemistry PYQs in the ViJEEta bank (NEET 2013–2026). It ranks 15 of 26 Chemistry chapters.

Take the 25-question Some Basic Concepts of Chemistry test Formula sheet ↓All NEET Chemistry chapters

3.4/100 Weight in Chemistry

Exam importance (3/5, by past-paper share)

24 NEET PYQs

417 Practice questions

373 With measured difficulty

How the weight is computed: this chapter's tagged NEET PYQs divided by all tagged NEET Chemistry PYQs in the bank (24 of 707), times 100, with repeated questions counted once. The bank does not store the year of each NEET question, so none is printed. Computed from the bank at build time. Updated 19 Oct 2026.

Some Basic Concepts of Chemistry: formula sheet for NEET

14 formulas, each with when to use it. Copy it onto one page of your notebook: that page is this chapter's handbook.

Number of moles
$n = \frac{given mass (g)}{molar mass (g mol ^{- 1} )}$
Use it when: Any mass is given and you need moles, which is the first step of almost every problem.
Number of particles
$N = n \times N_{A}$
$N_{A} = 6.022 \times 1 0^{23} mol^{- 1}$
Use it when: The question asks for atoms, molecules, ions or formula units.
Molar volume of a gas
$1 mol gas \leftrightarrow 22.7 L at STP (the NCERT value)$
Use it when: A gas volume at STP is given or asked.
Stoichiometric ratio
$moles of B = moles of A \times \frac{coefficient of B}{coefficient of A}$
Use it when: Going from one reactant or product to another, using a balanced equation only.
Limiting reagent
The limiting reagent is the reactant used up first; all product is calculated from it alone.
Use it when: Amounts of two or more reactants are given.
Molarity
$M = \frac{moles of solute}{volume of solution (L)}$
Use it when: Concentration is per litre of solution (it changes with temperature).
Molality
$m = \frac{moles of solute}{mass of solvent (kg)}$
Use it when: Concentration is per kg of solvent (it does not change with temperature).
Dilution
$M_{1} V_{1} = M_{2} V_{2}$
Use it when: Only water is added, so moles of solute stay the same.
Mole fraction
$x_{A} = \frac{n _{A}}{n _{A} + n _{B}}$
$x_{A} + x_{B} = 1$
Use it when: The ratio of moles of one component to total moles is asked.
Mass per cent of a solution
$mass % = \frac{mass of solute}{mass of solution} \times 100$
$mass of solution = solute + solvent$
Use it when: w/w % is given or asked.
Mass % of an element
$mass % of element = \frac{mass of that element in 1 mol of compound}{molar mass of compound} \times 100$
Use it when: Finding percentage composition or checking purity.
Molecular formula
$molecular formula = n \times empirical formula$
$n = \frac{molar mass}{empirical formula mass}$
Use it when: % composition is given (take 100 g, get moles of each element, divide by the smallest, make whole numbers).
Average atomic mass
$average atomic mass = \sum (fractional abundance \times isotope mass)$
Use it when: Isotopes and their abundances are given (convert % to fraction first).
Atomic mass unit
$1 u = \frac{1}{12} of the mass of one^{12} C atom = 1.66056 \times 1 0^{- 24} g$
Use it when: Converting the mass of a single atom between u and grams.

Trap

in molality you divide by the mass of solvent in kg, not the mass of the solution. Find solution mass = density × volume, then subtract the solute mass before dividing. Molarity is the other way round: litres of solution, not of solvent.

How does NEET ask Some Basic Concepts of Chemistry?

8 real previous-year questions from this chapter, as printed in the paper, each with its worked solution. Answer the first one here with no sign-in.

Q1ChemistryNEET UG PYQChemical Equations and Stoichiometry

Try right here · No sign-in

When 22.4 litres of H2(g) is mixed with 11.2 litres of Cl2(g), at S.T.P., the moles of HCl(g) formed is equal to

Answer key (C) & worked solution

Correct answer: Option C

_{2}

(g) + Cl

_{2}

(g) → 2HCl(g) Initial vol. 22.4L 11.2L ∴ 22.4 L volume at STP is occupied by Cl

_{2}

= 1 mole ∴ 11.2 L volume will be occupied by mole = 0.5 mole Thus,

1 m o l e H_{2} (g) + 0.5 C l_{2} (g) \to 2 H C l (g)

Since Cl

_{2}

possesses minimum number of moles, thus it is the limiting reagent. As per equation, 1 mol Cl

_{2}

≡ 2 mol HCl ∴ 0.5 mol Cl

_{2}

≡ 1 mol HCl Hence, 1.0 mole of HCl (g) is produced by 0.5 mole of Cl

_{2}

Q2ChemistryNEET UG PYQChemical Equations and Stoichiometry

1.0g of Magnesium is burnt with 0.56 g of O

_{2}

in closed vessel. Which reactant is left in excess and how much? (At.wt. Mg = 24; O = 16)

AMg, 0.44 g

_{2}

, 0.28 g

CMg, 0.16 g

_{2}

, 0.16 g

Answer key (C) & worked solution

Correct answer: Option C

2 Mg (1g) + O

_{2}

(0.56g) → 2MgO 32g oxygen reacts with = 2 × 24g Mg 0.56g oxygen reacts with = 0.84g Mg Mg is in excess Mg left = 1-0.84 = 0.16 g

Q3ChemistryNEET UG PYQAtomic and Molecular Masses

Suppose the elements X and Y combine to form two compounds XY

_{2}

and X

_{3}

_{2}

. When 0.1 mole of XY

_{2}

weighs 10 g and 0.05 mole of X

_{3}

_{2}

weighs 9g, the atomic weights of X and Y are

A60, 40

B20, 30

C30, 20

D40, 30

Answer key (D) & worked solution

Correct answer: Option D

Let atomic weight of X and Y be A

_{x}

and A

_{y}

respectively.

n_{X Y_{2}} = 0.1 = \frac{10}{A _{X} + 2 A _{Y}}

A_{X} + 2 A_{Y} = 100

… (1)

n_{X_{3} Y_{2}} = 0.05 = \frac{9}{3 A _{X} + 2 A _{Y}}

3 A_{X} + 2 A_{Y} = 180

… (2) on solving eq. (1) and (2)

A_{X} = 40, A_{Y} = 30

Q4ChemistryNEET UG PYQMole Concept

A mixture of gases contains H

_{2}

and O

_{2}

gases in the ratio of 1:4 (w/w). What is the molar ratio of the two gases in the mixture?

A2 : 1

B1: 4

C4: 1

D16: 1

Answer key (C) & worked solution

Correct answer: Option C

\frac{W _{H} _{2}}{W _{O} _{2}} = \frac{1}{4}; \frac{n H _{2}}{n O _{2}} = \frac{W _{H} _{2}}{W _{O} _{2}} \times \frac{M _{O} _{2}}{M _{H} _{2}} = \frac{1}{4} \times \frac{32}{2} = 4

Q5ChemistryNEET UG PYQMatter and Its Nature

Which of the following is a sink for CO?

AOceans

BPlants

CHaemoglobin

DMicro organisms present in the soil

Answer key (D) & worked solution

Correct answer: Option D

Micro-organisms present in the soil is a sink for CO.

∴

Any medium which will have capability to consume carbon monoxide will act as a sink.

Q6ChemistryNEET UG PYQReactions in Aqueous Media and Strength of Solution

Match the following and identify the correct option. (a)

C O (g) + H_{2} (g)

(i)

M g (H C O_{3})_{2} + C a (H C O_{3})_{2}

(b) Temporary hardness of water(ii) An electron deficient hydride(c)

B_{2} H_{6}

(iii) Synthesis gas(d)

H_{2} O_{2}

(iv) Non-planar structure

a - iii; b - i v; c - ii; d - i

a - i; b - iii; c - ii; d - i v

a - iii; b - i; c - ii; d - i v

a - iii; b - ii; c - i; d - i v

Answer key (C) & worked solution

Correct answer: Option C

\Rightarrow C O (g) + H_{2} (g) =

Water gas or synthesis gas

\Rightarrow

Temporary hardness of water is due to bicarbonates of

C a^{2 +} + M g^{2 +}

\Rightarrow

B_{2} H_{6}

is a electron deficient compound due to presence of banana bond.

\Rightarrow H_{2} O_{2}

open book like structure which is non-planar

Q7ChemistryNEET UG PYQMole Concept

Which one of the following has maximum number of atoms?

A1g of

O_{2} (g)

(Atomic mass of O = 16)

B1g of Li (s) (Atomic mass of Li = 7)

C1g of Ag (s) (Atomic mass of Ag = 108)

D1g of Mg (s) (Atomic mass of Mg = 24)

Answer key (B) & worked solution

Correct answer: Option B

(1) No. of atoms in O

_{2}

= \frac{1}{32} \times 2 \times N_{A}

(2) No. of atoms in Li

= \frac{1}{7} \times N_{A}

(3) No. of atoms in Ag

= \frac{1}{108} \times N_{A}

(4) No. of atoms in Mg

= \frac{1}{24} \times N_{A}

∴

1 gm of Li is having maximum no. of atoms.

Q8ChemistryNEET UG PYQChemical Equations and Stoichiometry

The number of moles of hydrogen molecules required to produce 20 moles of ammonia through Haber’s process is :

A20

B30

C40

D10

Answer key (B) & worked solution

Correct answer: Option B

Haber's process

N_{2} (g) + 3 H_{2} (g) ⇌ 2 N H_{3} (g)

20 moles need to be produced 2 moles of NH

_{3}

→ 3 moles of H

_{2}

Hence 20 moles of

N H_{3} \to \frac{3 \times 20}{2} = 30

moles of H

_{2}

Which topics in Some Basic Concepts of Chemistry carry the most questions?

The 12 busiest of 18 topics, by tagged PYQs, then practice questions. Counted from the bank. Updated 19 Oct 2026.

Topic	PYQs	Practice questions
Mole Concept	7	97
Chemical Equations and Stoichiometry	7	48
Reactions in Aqueous Media and Strength of Solution	2	52
Empirical and Molecular Formulae	2	45
Matter and Its Nature	2	13
Atomic and Molecular Masses	1	18
Physical Quantities and Their Measurements in Chemistry	1	12
Miscellaneous Examples	1	6
Dalton's Atomic Theory	1	4
Equivalent Concept	0	35
Laws of Chemical Combination	0	23
Limiting Reagent and Excess Reactant	0	16

Why does Some Basic Concepts of Chemistry show "–" until you answer 3 questions?

Unknown is not zero. Until you answer at least 3 graded questions in Some Basic Concepts of Chemistry, ViJEEta shows – instead of a zero or a 50% default. Book exercises can raise chapter mastery up to 0.60, adaptive practice up to 0.75, and only a timed chapter test or mock can certify 0.80 and above.

How ViJEEta scores you

What happens when you test Some Basic Concepts of Chemistry?

Every chapter test is 25 questions. It starts at moderate difficulty and adapts after each saved answer. If you open a solution before answering, that attempt earns no credit, so your mastery stays honest.

Start the Some Basic Concepts of Chemistry test

Chapters either side of Some Basic Concepts of Chemistry by weight

p-Block Elements (Group 15 to 18) Weight 3.5/100 Ionic Equilibrium Weight 3.4/100 Structure of an Atom Weight 3.4/100 Classification of Elements and Periodicity Weight 3.1/100

Some Basic Concepts of Chemistry: NEET PYQs and weightage

Some Basic Concepts of Chemistry: formula sheet for NEET

Number of moles

Number of particles

Molar volume of a gas

Stoichiometric ratio

Limiting reagent

Molarity

Molality

Dilution

Mole fraction

Mass per cent of a solution

Mass % of an element

Molecular formula

Average atomic mass

Atomic mass unit

How does NEET ask Some Basic Concepts of Chemistry?

Which topics in Some Basic Concepts of Chemistry carry the most questions?

Why does Some Basic Concepts of Chemistry show "–" until you answer 3 questions?

What happens when you test Some Basic Concepts of Chemistry?

Chapters either side of Some Basic Concepts of Chemistry by weight