○　正解です。

In English 'if' is used when we don't know what will happen.
For example : If it is sunny tomorrow, let's play soccer.
We don't know about tomorrow's weather so we use 'if' in this sentence.

When is used when we do know what will happen.
For example : I will wake up when the sun rises tomorrow.
Every morning the sun rises and I know it will rise again tomorow, so we should use when in this sentence.