The image shows a Lithium Atom. The atom is composed by three subatomic particles: electron, proton and neutron.
The number of protons in an atom gives the type of atom it is. The Lithium atom has an atomic number of 3, which means that this atom always has 3 protons.
The protons and the neutrons are in the nucleus of the atom, which are , in this case, the blue and red particles. We can see that we have 4 blue ones, and since we know that we can only have 3 protons on Lithium, the blue ones have to be the neutrons, which males the red ones the protons.
The electrons are located around the atom, on the orbital, so they are the green ones.
Thus, we have:
1 - electron
2 - proton
3 - neutron