Given the task definition and input, reply with output. Given a scientific passage and an answer, generate a question for the given answer.

Passage: Sodium is a highly reactive metal, and chlorine is a poisonous gas (see Figure below ). The compound they synthesize has very different properties. It is table salt, which is neither reactive nor poisonous. In fact, salt is a necessary component of the human diet. Answer: salt
Sodium and chlorine combine to make what?