The correct answer is option 2, Jupiter. Jupiter is the largest planet in our solar system, with a diameter of about 143,000 kilometers. Let`s analyze the other options to understand why they are not correct.

Option 1, Mars, is incorrect because Mars is the fourth planet from the Sun and is much smaller than Jupiter.

Option 3, Saturn, is also incorrect. While Saturn is a large planet, it is not as large as Jupiter.

Option 4, Mercury, is the smallest planet in our solar system. It is much smaller than both Jupiter and Saturn.

Therefore, the largest planet in our solar system is indeed Jupiter, making option 2 the correct answer.