Answer:
The statements that describe the planets are:
Mars and Venus are mostly rock.
Saturn is classified as a gas giant
Earth is much smaller than Uranus.
Step-by-step explanation:
Mars and Venus are the fourth and second planets from the sun respectively. These planets along with a few others in our solar system are classified as terrestrial planets because of the compact rock that makes up its surface. For this reason, the statement that Mars and Venus are mostly rock is correct
The ancient Greeks were pioneers in the field of astronomy, their discoveries lead to much of what we know today about our solar system. Despite this, only five planets were discovered by them. Some discoveries like
Neptune
Uranus
Pluto (No longer a planet)
are not credited to the ancient Greeks. This makes the statement, "The ancient Greeks discovered all the planets in the solar system" false.
Saturn and Jupiter are classified as gas giants because they are made up primarily of gases like hydrogen and helium. This tells us that "Saturn is classified as a gas giant." is true, and "Jupiter is mostly rock surrounded by clouds." is false.
Pluto is considered a dwarf planet does not discribe the planets because the current scientific consensus is that pluto does not meet the minimum requirements to be considered a planet, since the scientific community agrees that "Planets" and "dwarf planet" describe separate entities. However, the statement itself is true. Though not considered a planet, it has been given the status of "dwarf planet".
The final statement, "Earth is much smaller than Uranus." is true because Uranus has a diameter four times greater than the earth.
The statements that Mars and Venus are mostly rock and Saturn is a gas giant are true due to the composition of these planets. We also consider that Earth is much smaller than Uranus because Earth has only one-fourth of the diameter of Uranus and only 6% of its surface area. The remaining statements are untrue.