This is about how to ask the percentage of alcohol in a drink in casual conversation.

For example, you and your friend are in a restaurant or a bar. Your friend loves alcohol and knows a lot about it. You don't know much about alcohol. You look at the drink your friend is having, and would you say:

1. What percentage of alcohol does it contain?
2. What's the percentage?
3. How strong is it?

If the above sentences are unnatural, please tell me more natural ways to say it. Thank you.