I do I figure out which bond is longest

a. C-F
b. C-N
c. Si-Se
d. C≡N
e. Si-Br

The answer is c. but I don't understand??? Please answer quick. Thanks.

2 answers

Long bonds mean weak bonds, which occur between elements very close in the Periodic table.
wait how is Si and Se closer to each other than C-N, they are right next to each other, and what about with double and triple bonds? Thanks.