Question

Which expression correctly represents a balanced reduction half-reaction?

Answer 1

for answering for the question, there exists four choices:
1) Na+  +  e- -------------- Na
2) Na --------Na+   +  e-
3) Cl2 +   2e-  ------------ Cl-
4) 2Cl-  ---------Cl2 +  2e-

reduction half-reaction general formula is 
oxidant + e - or +  -------- Product

so in our case the answer is 
1) Na+  +  e- -------------- Na (exactly balanced)