What is the difference between a molecule and a compound and an atom, need help

Explanation:

An atom is the smallest building block of all matter that exists singly. Like sodium atoms.

A molecule could be either a group of atoms of the same element, like oxygen (O2) OR a group of atoms of different elements like all compounds (eg. carbon dioxide, CO2).

A compound is a molecule made of atoms of different elements joined by chemical bonds. Like water (H2O), table salt (NaCl).

1. b.

2. d.

3. a.

5. d.

6. c.

these are the only ones that i know, i hope this , and good luck.