Answer
b, d
Work Step by Step
In a, c, and e, an elemental form of a compound is being separated into single-atom form. The elemental form has lower chemical potential energy than monatomic form; that is why the compound is found naturally in that form, so the process would be endothermic. For b, a liquid is turning into a solid, so potential energy from phase change is released. For d, this is the formation of water, which is exothermic.
