NEETChemistryPractical Chemistry
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): When dilute H ₂ SO ₄ is added to a solid nitrite salt, the gas evolved is initially colourless inside the liquid but turns into reddish-brown fumes at the mouth of the test tube. Reason (R): Nitrite reacts with dilute acid to yield colourless nitrous oxide ( N ₂ O ) gas, which is rapidly oxidized b
Options
- ABoth (A) and (R) are true and (R) is the correct explanation of (A)
- BBoth (A) and (R) are true but (R) is not the correct explanation of (A)
- C(A) is true but (R) is false
- D(A) is false but (R) is true
Correct answer
C. (A) is true but (R) is false
Step-by-step solution
The assertion is a true factual observation from qualitative analysis. When dilute H ₂ SO ₄ is added to a nitrite salt, a colourless gas is initially evolved which turns brown at the mouth of the test tube. The reason is false. Nitrite reacts with dilute acid to yield nitric oxide ( NO ), not nitrous oxide ( N ₂ O ). NO is a colourless gas that is rapidly oxidized by atmospheric oxygen to form brown nitrogen dioxide ( NO ₂ ). The reactions are: 3 NO ₂^- + 2 H ^+ NO ₃^- + 2 NO + H ₂ O 2 NO + O ₂ 2 NO ₂ (brown fumes)