Xwhy is cyano group called as an
ambident group?

Both the C and the N can participate in reactions  

Explanation:

The word ambident comes from two Latin words that mean "both teeth".

An ambident group can react at two different sites to form products.  

For example, the cyano group has two major resonance structures (see below).

The hybrid has two different ends, each with a lone pair and a partial negative charge.

Thus, it can react to form CH₃CN by having the C attack, or CH₃NC by having the N attack.

the answer your looking for is c).