Why is cyanide ion negatively charged?

The cyanide is 
A carbon atom has 4 valance electrons and nitrogen has 5. Below is a Lewis-dot-structure of cyanide.
:N≡C.
The carbon atom is still one electron short of having a full octet and so it will seize another electron from almost anything, making the cyanide ion negative and whatever it took the electron from it now positive.

Adozen is 1221/12 = 1.751.75 x 12 = 21therefore, 1.75 is the answer.