Fill in the blanks with the most appropriate option:-

If the world ended tomorrow, I __________ be very sad.

would

The most appropriate option to fill in the blanks is would.

The sentence "If the world ended tomorrow, I would be very sad" is in the second conditional, which is used to talk about hypothetical situations. The other options are not as appropriate.

• Will is used to talk about future events that are certain to happen. This does not make sense in the context of the sentence, as the world ending tomorrow is not a certain event.
• Shall is used to make a formal request or to express determination. This does not make sense in the context of the sentence, as the speaker is not making a formal request or expressing determination.
• May is used to express possibility. This does not make sense in the context of the sentence, as the speaker is not expressing possibility, but certainty.