Which of the following reactions involves sharing electrons?
a. decomposition
c. synthesis
b. neutralization
d. combustion

I think the best answer from the options is C. A synthesis reaction is the one that involves sharing of electrons because many reactants forms to one single product. This type of reaction releases energy mostly in the form of heat or light therefore it is an exothermic reaction.

1. Ca(s)

2. Co(s)

3. Cs(s)

4. Cu(s)

Answer is 3. Cs(s)