Question

Assertion: NaCl reacts with concentrated $H_{2}S{O}_4$ to give colourless fumes with a pungent smell. But on adding $Mn{O}_2$, the fumes become greenish yellow.
Reason: $Mn{O}_2$ oxidises HCl to chlorine gas which is greenish yellow.

• A. Both assertion and reason are correct statements, and reason is the correct explanation of the assertion
• B. Assertion is wrong but reason is correct statement.
• C. Assertion is correct but reason is wrong statement.
• D. Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion
• E. Both assertion and reason are wrong statements.

Answer 1

The correct option is A Both assertion and reason are correct statements, and reason is the correct explanation of the assertion

Analyzing the assertion

NaCl reacts with concentrated $H_{2}S{O}_4$ and following reaction takes place:

$2NaCl+H_{2}S{O}_4\to N{a}_{2}S{O}_4+2HCl$

Thus when NaCl reacts with concentrated $H_{2}S{O}_4$ hydrochloric gas (HCl) is produced as a by-product.

On adding $Mn{O}_2$, reaction will take place as:

$Mn{O}_2+4HCl\to MnC{l}_2+2H_{2}O+C{l}_2$

Thus, $Mn{O}_2$ oxidizes HCl to chlorine gas $\left(C{l}_2\right)$.
So, the assertion is correct.

Analyzing the reason

In HCl ,Cl has -1 oxidation state and in $C{l}_2$, it has zero oxidation state. Hence, one can say that $Mn{O}_2$ oxidizes HCl to $C{l}_2$ gas.
The greenish yellow fumes are of chlorine gas since it is yellowish green in appearance.
So, reason is also correct.

Hence, assertion and reason both are correct, and reason is the correct explanation of assertion.

Hence, option (A) is correct.