Answer : 4. "must"
Explanation :

Let’s look at how the given modal verbs are used:

• Ought to – When there is a strong sense of moral duty, advice, or indication of correc action.

Example: You ought to serve your motherland.

• Must- “Must” is a modal verb most commonly used to express certainty. It can also

be used to express necessity or strong recommendation, although native speakers prefer the more flexible form “have to.”.

Example: You must follow the instructions.

• Should- used to show obligation, duty, or correctness.

Example: One should obey one’s parents.

• Might- We use might most often to refer to weak possibility.

Example: I might go to Japan for a month to study Japanese.

• The sentence is expressing some kind of certainty. So ‘Must’ is used here.

The correct sentence is: You must be mad if you think I’m going to lend you any more money.