Ncert Exercises & Solutions

Given below are two statements:

Assertion (A):	Conc HNO₃ makes iron passive.
Reason (R):	HNO₃ forms a protective layer of ferric nitrate on the surface of the iron.

1.	Both (A) and (R) are true and (R) is the correct explanation of (A).
2.	Both (A) and (R) are true but (R) is not the correct explanation of (A).
3.	(A) is true but (R) is false.
4.	(A) is false but (R) is true.

HINT: Passive means metal became non-reactive.

Explanation:

Explanation: When iron (Fe) reacts with concentrated nitric acid (HNO₃), it indeed becomes passive. This means that iron stops reacting with the acid after a certain point because a protective oxide layer forms on the surface, which prevents further corrosion. This layer acts as a shield, making iron resistant to further oxidation or corrosion by nitric acid. This phenomenon is called passivation, and HNO₃ is known to make iron passive.

So, Assertion (A) is true.

Explanation: This part of the statement is not fully accurate. While HNO₃ does indeed form a protective layer on the iron, this layer is primarily composed of iron oxides (mainly ferric oxide, Fe₂O₃) rather than ferric nitrate (Fe(NO₃)₃). Ferric nitrate is a soluble salt, not the solid oxide layer that actually provides the protective barrier. So, the description in Reason (R) is incorrect because it mentions ferric nitrate, which is not the protective layer that forms in the passivation process.