The correct option is A waiting
Let’s examine the sentence: “I don't mind ____ for you.” The sentence specifies a state of action that is to be the speaker does not ‘mind. ‘As the sentence talks about the state of action, and not the action itself, it requires a noun or a gerund. The gerund always has the same function as a noun (although it looks like a verb). The gerund ends in ‘ing.’ As Option B fulfils this requirement, so it is the correct answer. All the other options cannot be used as they would make the sentence meaningless.