Fill in the blank in the following sentence with the most appropriate…

The correct answer is Option (4) → will you

Question tag after an imperative:

• An imperative sentence (an order, request or invitation) has no stated subject. Its tag uses you.
• The usual tag for an imperative is will you? (for an invitation, "won't you?" is also used).
• "Have some more rice" is an invitation, so the tag is will you.
  Complete sentence: Have some more rice, will you?

Why the Other Options are Incorrect?

Option 1: wouldn't you — Incorrect. Wouldn't you follows a sentence with "would" ("You would like some rice, wouldn't you?"), not an imperative.

Option 2: can you — Incorrect. Can you asks about ability and suits a request for help, not an offer of food.

Option 3: did you — Incorrect. Did is past tense and goes with a statement about the past ("You had rice, didn't you?").