Which of the following is an example of an idiom

A cold day in July// a snowball’s chance in hell// all wet// over the mood// goose is cooked// can of worms. Hope I helped

B - to tell a white lie.

Explanation:

An idom means something different from the actual words used (raining cats and dogs) and can't be literal. When you tell a lie - there aren't actually colors associated with them, so you cannot 'literally' tell a lie and have it appear to be white.