Which of the following sentences is correct?

The correct answer is Option (3) → The seeds of a papaya are much smaller than those of a ripe jackfruit.

Comparing like with like: “that of / those of”:

• When we compare, both sides must be the same kind of thing. Here seeds are compared with seeds.
• “Those of a ripe jackfruit” means “the seeds of a ripe jackfruit”. We use those because “seeds” is plural (“that” is for a singular noun).

Why the Other Options are Incorrect?

Option 1: Meena, as well as her two brothers, are learning to swim at the club this summer. — Incorrect. With “as well as”, the verb agrees with the first subject. Here that is “Meena”, which is singular.
Corrected: Meena, as well as her two brothers, is learning to swim at the club this summer.

Option 2: The new gym in our colony has all the latest equipments for weightlifting. — Incorrect. “Equipment” has no plural form. It never takes -s.
Corrected: The new gym in our colony has all the latest equipment for weightlifting.

Option 4: In the meeting, the class monitor discussed about the picnic plan with our teacher. — Incorrect. “Discuss” takes its object directly, without “about”.
Corrected: In the meeting, the class monitor discussed the picnic plan with our teacher.