Prepositions are dropped before common question words. This usually happens after common verbs like tell, ask, depend, sure, idea and look. This is especially common in indirect questions.
- Tell me about your plans. (Here we use the preposition about before the noun ‘your plans’.)
- Tell me what you intend to do. (More natural than ‘Tell me about what you intend to do’.) (Here the preposition is dropped before the question word what.)
- I asked her about her relationship status.
- I asked her whether she was in a relationship. (NOT I asked her about whether she was in a relationship.)
- She may win the prize – it depends on her performance.
- She may win the prize – it depends (on) how well she performs.
- Look at this.
- Look (at) what I have brought for you.
The prepositions cannot normally be left out after other verbs.
- I am worried about her health.
- I am worried about how she is going to cope. (NOT I am worried how she is going to cope.)
- The teacher asked me what I had done. (More natural than ‘The teacher asked me about what I had done’.)
- The police questioned me about what I had seen. (NOT The police questioned me what I had seen.)
- Your chances of getting a good job can vary according to whether you live in a city or in a village.
Note that we cannot put if after a preposition. We use whether instead.
- I am worried about whether she is happy. (NOT I am worried about if she is happy.)