Which of the following metal atoms would have the highest conductivity?

Conductivity is a way that an atom reacts. Therefore, when we say "highest" we mean the most reactive. Elements or atoms that are highly reactive are those that want to be stable. Therefore, the atoms that have 7 valence electrons would be highly reactive because they need 1 more electron to fill their outer energy shell to become stable. 

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