Given below are two statements: 

Assertion (A): 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.
HNO3 makes iron passive due to the formation of a reddish-brown layer of iron oxide which prevents its further reaction with
the acid. Nitric acid forms iron oxide, not ferric nitrate. 
The process of formation of this protective layer because of concentrated nitric acid is known as Passivation. Hence, the metal becomes chemically passive because of reacting with concentrated nitric acid.
Hence, Assertion is correct, but Reason is the wrong statement.