plz help me fast

Dear student,
Please find below the answer:

The correct option is (a) i.e. both assertion and reason are true and the reason is the correct explanation of assertion.
Interferons are chemical signalling molecules that are released in response to viruses, bacteria, parasites etc. A virus-infected cell release interferons in response to virus infection and the released interferons inhibit the adjacent cells from virus infection, thus acting as anti-viral defence molecules.  

Hope this clears your doubt.
Regards.