Question

What is zero conditional if clause?

Answer 1

We use the zero conditional when we want to talk about facts or things that are generally true. Scientific facts are often covered by the zero conditional: "When you heat ice, it melts." The zero conditional uses if or when and must be followed by the simple present or imperative.

Answer 2

We use the zero conditional when we want to talk about facts or things that are generally true. ... The zero conditional uses if or when and must be followed by the simple present or imperative. For example: "When it rains, tennis lessons are held in the gym." "If it rains, tennis lessons are held in the gym."