Which is the best description of a molecule? A molecule of an element is composed of at least two types of atoms.
B molecule of a compound is composed of only one type of atom.
C molecule of a compound is composed of at least two types of atoms.
D molecule of an element is composed of exactly two types of atoms.

By definition, we have to:
A molecule is a group of at least two atoms in a defined configuration linked by chemical bonds.
We have two types of molecules:
1) several atoms of a single chemical element, as in the case of oxygen. (O2)
2) Atoms of different elements, as in the case of water. (H2O)

the best description of a molecule is:
A: A molecule of an element is composed of at least two types of atoms.

Work done = force ×distancebut force = mass ×gravityand gravity = 10m\s force = 2×10 = 20 work done = 20×3 = 60 joules