What is a good hook for hair gel and hair spray(like a good one for a science fair ) that makes sense

An exothermic reaction is conducted in an insulated calorimeter filled with water. the calorimeter is then sealed so that there is no heat exchanged between the contents of the container and the surrounding air. which of the following statements is true about the reaction?

Can someone me with questions 15 to 17 plz.

Which diagram shows the correct way to represent an ionic compound of magnesium oxide?