JEE Advanced 2022 Paper 1 Q12 Chemistry Inorganic Chemistry p-Block Elements (Groups 15-18) Medium

JEE Advanced 2022 Paper 1 · Q12 · p-Block Elements (Groups 15-18)

The treatment of galena with HNO$_3$ produces a gas that is

  1. A. paramagnetic
  2. B. bent in geometry
  3. C. an acidic oxide
  4. D. colorless
JEE Advanced multi-correct — pick every correct option, then check.
Reveal answer + step-by-step solution

Correct answer:A, D

Solution

Galena is PbS. Treatment with dilute HNO$_3$ proceeds via redox: 3 PbS + 8 HNO$_3 \rightarrow$ 3 Pb(NO$_3$)$_2$ + 3 S$\downarrow$ + 2 NO$\uparrow$ + 4 H$_2$O. The gas produced is nitric oxide, NO.

(A) TRUE. NO has 11 valence electrons; it is an odd-electron molecule with one unpaired electron, hence paramagnetic.

(B) FALSE. NO is a linear (diatomic) molecule — diatomic molecules are linear by definition; "bent geometry" does not apply.

(C) FALSE. NO is a neutral oxide (neither acidic nor basic); it does not react with bases to form salts. (NO$_2$ and N$_2$O$_5$ are the acidic nitrogen oxides.)

(D) TRUE. NO is a colourless gas at the moment of formation (it turns brown in air due to oxidation to NO$_2$).

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