Consider this statement: earth is the only source of gravity in the solar system. do you agree? give your reasons.

No, everything with a mass has gravity. That's why the planets orbit the sun. That's why moons orbit planets. The asteroid belt etc etc. If you drop something heavy on the moon, it'll still fall to the ground, this proves that there is gravity on the moon. The Mars rover is still on Mars, it hasn't floated away, this proves there is gravity on Mars.

The metal is named first