The correct answer is option 2: Planets between the sun and the belt of asteroids.

The inner planets are the ones that are located closer to the sun in our solar system. These planets include Mercury, Venus, Earth, and Mars. They are called inner planets because they are situated between the sun and the asteroid belt, which is a region located between the orbits of Mars and Jupiter.

Option 1, which suggests that the inner planets are the ones between the sun and the Earth, is incorrect as it does not include Venus and Mercury, which are also inner planets.

Option 3, which states that the inner planets are the ones near the Earth, is not accurate as it also leaves out Mercury and Venus.

Option 4, which mentions that the inner planets are the ones around the sun, is too broad as it includes all the planets in our solar system, even the outer ones.

Therefore, option 2 is the correct choice as it accurately defines the inner planets as the ones situated between the sun and the asteroid belt.