Chemical reactions that release energy
a. will not occur.

b. need catalysts to occur.

c. will always explode.

d. often occur spontaneously.

I do not feel comfortable with this question. You should not use words like often, or even always, in a multiple choice question.

Certainly some reactions that do release energy occur spontaneously and some do not, you cannot state how ofthen this happens.

You might think that this is frequent, because when a chemical process release energy the products will be more stable than the reactants. But the real driver is the Activation Energy. If a chemical reaction has a high activation energy, it will need a trigger (may be a catalyst or to supply energy to the reactants) to make the equation happen.

Also, some reactions that release energy, may explode, althoug there are a lot that not.

Having said that, I would choose the option D: "often occurs spontaneously", becasue many of them do (you cannot tell how many does and how many does not). 

Use a magnet to separate iron, evaporate water, i'm not sure how to separate the other two i'm sorry but good luck

The answers are 3.c kelvin4.b liquids only