1. Sweetheart, did you apply the cosmetics/lotion on your face?

Question

2. Sweetheart, did you wear the cosmetics/lotion on your face?

3. Sweetheart, did you put the cosmetics/lotion on your face?

(What about the expressions? Are all expressions grammatical? Do we have to use the singular form 'cosmetic' or the plural form 'cosmetics' in this case?)

Answer 1

The first and third are good; I guess the second one is, too. But the third one is the most commonly used. And yes, it's "cosmetics."