Explanation:

National emergency can be declared under A352 on the basis of external aggression or armed rebellion in the whole of India or a part of its territory. Such an emergency was declared in India in 1962 (Indo-China war), 1971 (Indo-Pakistan war), and 1975 (declared by Indira Gandhi). The President can declare such an emergency  only on the basis of a written request by the Council of Ministers headed by the Prime Minister. Such a proclamation must be laid before both houses of Parliament, and the state of emergency expires after one month unless approved within that time by both houses sitting and voting separately. It is not declared in case of epidemics, natural calamities or failure to form government at the Centre which makes all options other than (b) wrong.