Which is the biggest planet?
a. Venus
b. Mars
c. Mercury
d. Jupiter

Hint: The Solar System is the Sun and all the heavenly bodies that orbit around it, including the eight planets, their moons, the asteroids and comets.

Complete Answer:
Let us analyze the options given to us in this question -
Option (a.), 'Venus', refers to ‘the second nearest planet to the sun; it is peculiar in that its rotation is slow and retrograde (in the opposite sense of the Earth and all other planets except Uranus); it is visible from Earth as an early `morning star' or an `evening star'’.
Therefore, option (a.) is incorrect as it is not the largest planet in the solar system.
Option (b.), ‘Mars', refers to ‘a small reddish planet that is the 4th from the sun and is periodically visible to the naked eye; minerals rich in iron cover its surface and are responsible for its characteristic color’.
Therefore, option (b.) is incorrect as it is not the largest planet in the solar system.
Option (c.), ‘Mercury', refers to ‘the smallest planet and the nearest to the sun’.
Therefore, option (c.) is incorrect as it is not the largest planet in the solar system.
Option (d.), ‘Jupiter', refers to ‘the largest planet and the 5th from the sun; has many satellites and is one of the brightest objects in the night sky’.
Therefore, option (d.) is correct as it is the largest planet in the solar system.

Note: In the solar system, a planet is any of the nine large celestial bodies in the solar system that revolve around the sun and shine by reflected light; otherwise, it is any celestial body (other than comets or satellites) that revolves around a star.