Assertion (A): NaCl reacts with concentrated H2SO4 to give colourless fumes with a pungent smell. But on adding MnO2, the fumes become greenish-yellow.

Reason (R): MnO2 oxidizes HCl to chlorine gas which is greenish-yellow.

1. Both the assertion and the reason are correct statements and the reason is the correct explanation of the Assertion.

2. Both the assertion and the reason are correct statements and the reason is not the correct explanation of the Assertion.

3. The assertion is correct but the reason is the wrong statement.

4. The assertion is incorrect but the reason is a correct statement.

HINT: Colourless fumes with a pungent smell gas is HCl
Explanation:
NaCl reacts with concentrated H2SOto give colourless fumes with a pungent smell. 
The pungent smell is due to the formation of HCl. The reaction is as follows:
NaCl + H2SO4  Na2SO4 + 2HCl
But on adding MnO2 the fumes become greenish-yellow due to the formation of chlorine gas. MnO2 oxidised Cl- into Cl2.
The reaction is as follows:
MnO2 + 4HCl → MnCl2 + 2H2O + Cl2