Your answer : How much rice do you eat?

The first sentence is correct.

I would say that they’re both correct but slightly different. The first sentence asks about the quantity of rice you eat, while the second asks about the frequency with which you eat rice. I might use the adverb often rather than much to ask about frequency, but much sounds ok, too.

How much rice do you eat? This is asking how often you eat rice. This expects an answer like, you eat it a few meals every week. It could also be asking how much is eaten at this meal. This would expect an answer like, I can eat a cup full of rice. Other ways to ask; How often do you eat rice? Answer, three times per week. How much rice would you like with your meal? Answer, a cup full.

'How much rice do you eat?' That one sounds right🌟