The correct option is B Both assertion and reason are true but reason is not the correct
explanation.
Antivirals are compounds that are generally used to treat viral infections. Hence the "Reason" statement is true.
The "Assertion" statement is true. Common cold is caused by not just one virus but many differents kinds of viruses. Antivirals are generally specific in the viruses they target. Since there are too many viruses to target, antivirals are not used to treat common cold. Also, rapid mutation occurring in these viruses make it furthermore difficult to target.
Both statements are true, but the "Reason" is not the correct explanation for the "Assertion".