Nine planets revolve around the sun. The outer, distant planets are Jupiter, Saturn, Neptune, Uranus and Pluto. In comparison to these, the ‘inner planets’, Mercury, Venus, Earth and Mars that are nearer to the centre of the sun contain relatively:
(a) New elements of matter
(b) Lighter elements
(c) Heavier elements of matter
(d) Larger quantities of gas

Hint: Since the planets Jupiter, Saturn, Neptune, Uranus and Pluto are away from the Sun, their atoms composition (what they are made of) are different from that of the inner planets like Mercury, Venus, Earth and Mars. The outer planets are mostly gas giants.

Complete step by step answer:
The major difference between the inner and outer planets is the composition of which they are mostly made. While the inner planets are the ones before the asteroid belt in our solar system and near to the sun; they are Mercury, Venus, Earth, and Mars; the outer planets are Jupiter, Saturn, Uranus, Neptune and the dwarf planet Pluto. Now, the inner planets are closer to the sun and are rocky, the outer planets are far from the Sun and are mostly made of gases.
The four inner planets are called terrestrial planets because their surfaces are solid. They’re made up mostly of heavy metals such as iron and nickel, and have either no moons or few moons.
Thus option (c): heavier elements of matter, is the correct option.

Note:
This makes predicting how our Solar System formed an interesting exercise for astronomers. Conventional wisdom is that the young Sun blew the gases into the outer fringes of the Solar System and that is why there are such large gas giants there.Students can get a basic idea of the solar system first to understand this question better.