why do you think that sodium chloride has to be heated to 800c before melting, but candle wax will start to melt at 50c?

Sodium chloride is an ionic compound which makes it stronger and have a higher melting and boiling point. Candle wax is a covalent compound so it has a low melting point.

Explanation:

the answer is b because, investigating whether another species of moth also drinks tears might be interesting, but it would not directly explain why this species of moth does.

to explain why this species of moth drinks tears, the scientist could ask: "what nutrients that moths need are in elephant tears? "

the scientist could experiment with moth repellent or oter ways to keep the moths away, but that would not answer his original question.