1. Can I ask you a favor?

2. Can I ask you a thing?
3. Can I ask you two things?
4. Can I ask you two favors?
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favor: a thing that you do to help sb...

This was the definition of 'favor' according to a dictionary.

Can we use all the expressions above from 1 to 4? Does #1 mean #2?

All except question 2 are used.