NEET Chemistry important Questions— Set 1 (Physical Chemistry) — Solved (EN + HIN)

NEET Chemistry  — Set 1 (Questions 1–10)

Physical Chemistry focus: mole concept, gases, equilibria, kinetics, electrochemistry, colligative properties. Each solution gives a short English explanation followed by a Hinglish note.

Series: Set 2 (Org Basics) • Set 3 • Set 4 • Set 5

Q1. How many significant figures are in the measurement 0.004200?

(Physical chemistry — significant figures)

(a) 3

(b) 4

(c) 2

(d) 5

Answer — (b) 4 significant figures

English: Leading zeros are not significant; trailing zeros after the decimal are significant. So 0.004200 has digits 4,2,0,0 → 4 sig figs.

Hinglish: Aage ke zeros count nahi hote; decimal ke baad wale trailing zeros count hote hain. (इसलिए उत्तर b)।

Q2. 2.00 g of hydrogen reacts with excess O₂ to form water. How many moles of H₂O are produced? (Atomic masses: H = 1.00, O = 16.0)

(Stoichiometry)

(a) 1.00 mol

(b) 2.00 mol

(c) 0.50 mol

(d) 1.50 mol

Answer — (a) 1.00 mol

English: Moles of H₂ = mass / M = 2.00 / 2.00 = 1.00 mol. Reaction: \( \mathrm{H_2 + \tfrac12 O_2 \rightarrow H_2O} \) → 1 mol H₂ gives 1 mol H₂O.

Hinglish: H₂ ka mol 1 hai, aur reaction stoichiometry se 1 mol H₂ → 1 mol H₂O. (उत्तर a)।

Q3. One mole of an ideal gas at STP occupies 22.4 L. If temperature is doubled at constant pressure, volume becomes:

(Ideal gas law)

(a) 11.2 L

(b) 22.4 L

(c) 44.8 L

(d) 67.2 L

Answer — (c) 44.8 L

English: At constant pressure \( V \propto T \). If T doubles → V doubles: \(22.4 \times 2 = 44.8\) L.

Hinglish: Pressure constant pe volume temperature ke proportion mein badhta hai. Double T ⇒ double V. (उत्तर c)।

Q4. For reaction \( \mathrm{N_2 + 3H_2 \rightleftharpoons 2NH_3} \), if \(K_c = 1.6 \times 10^{-5}\) at a given T, the reaction lies predominantly:

(Chemical equilibrium)

(a) To the right (products)

(b) To the left (reactants)

(c) At equilibrium equally

(d) Not enough info

Answer — (b) To the left (reactants)

English: Small \(K_c\) (<<1 div="" equilibrium="" favored.="" left.="" lies="" means="" reactants="" so="" to="">

Hinglish: \(K_c\) chhota hai ⇒ reactants zyada stable hain; products kam. (उत्तर b)।

Q5. For the acid dissociation \( \mathrm{HA \rightleftharpoons H^+ + A^-} \), if \(K_a = 1.0\times10^{-5}\) and initial [HA] = 0.1 M, approximate pH of the solution (assume x small):

(Ionic equilibrium / approximations)

(a) 3.00

(b) 2.50

(c) 5.00

(d) 1.00

Answer — (a) pH ≈ 3.00

English: \(K_a = x^2/(0.1-x) \approx x^2/0.1\). So \(x = \sqrt{K_a\times0.1} = \sqrt{1e{-5}\times0.1} = \sqrt{1e{-6}} = 1e{-3}\) M. [H⁺]=10⁻³ ⇒ pH = 3.00.

Hinglish: Approximation se [H+] = 10⁻3 ⇒ pH 3. (उत्तर a)।

Q6. Rate law for reaction \( \mathrm{2A + B \rightarrow products} \) is experimentally found to be rate = k[A]²[B]⁰. The reaction order is:

(Chemical kinetics)

(a) 1

(b) 2

(c) 3

(d) Zero order

Answer — (c) 3 (third order)

English: Sum of exponents = 2 + 0 = 2? Wait: careful—rate = k[A]²[B]⁰ → exponent on B is zero, so order = 2 + 0 = 2 → second order. (Correct is 2)

Hinglish (clarify): Exponents ka sum order hota hai. Here 2 + 0 = 2 ⇒ second order. (उत्तर b)।

Q7. In electrochemistry, for the cell reaction at standard conditions, Nernst equation relates E to concentrations. If Q = 1, then E =:

(Electrochemistry / Nernst)

(a) E°

(b) E°/2

(c) 0

(d) −E°

Answer — (a) E°

English: Nernst: \(E = E^\circ - \dfrac{RT}{nF}\ln Q\). If Q = 1 ⇒ ln Q = 0 ⇒ E = E°.

Hinglish: Reaction quotient 1 par cell potential standard value E° hi rahega. (उत्तर a)।

Q8. Colligative property: The addition of non-volatile solute to solvent lowers vapor pressure. According to Raoult's law, the vapor pressure of solvent above solution is:

(Colligative properties)

(a) \(P^0_A\)

(b) \(x_A P^0_A\)

(c) \(x_B P^0_A\)

(d) \(P^0_A + x_BP^0_A\)

Answer — (b) \(x_A P^0_A\)

English: Raoult's law: partial pressure of solvent A over solution = mole fraction of A in liquid × vapor pressure of pure A: \(P_A = x_A P_A^0\).

Hinglish: Solvent ka vapour pressure mole fraction se reduce hota hai: \(P_A = x_A P_A^0\). (उत्तर b)।

Q9. Which of the following salts gives acidic solution in water?

(Acid-base character of salts)

(a) NaCl

(b) NH₄Cl

(c) KNO₃

(d) Na₂SO₄

Answer — (b) NH₄Cl

English: NH₄⁺ is the conjugate acid of weak base NH₃ and lowers pH; Cl⁻ is neutral. So solution acidic.

Hinglish: NH₄Cl mein NH₄⁺ acidic behaviour deta hai ⇒ acidic solution. (उत्तर b)।

Q10. Standard enthalpy of formation of element in standard state is:

(Thermochemistry)

(a) Zero

(b) 1 kJ mol⁻¹

(c) Negative

(d) Depends on element

Answer — (a) Zero

English: By convention, the standard enthalpy of formation of an element in its standard state (e.g., O₂(g), C(graphite)) is zero.

Hinglish: Element ka standard state le kar uska ΔHf° = 0 maana jata hai. (उत्तर a)।

Next: Set 2 (Organic Basics — Q11–Q20) • All Chemistry Set