Explain why a hydrogen atom can become either an ion or a part of molecule?

If it loses that 1 electron (0 electrons, 1 proton, 1 neutron) it become an ion that is positively charge because it has more protons than electrons. [Ignore the neutrons] 

If it gains an electron (2 electrons, 1 proton, 1 neutron) it becomes an ion that is negatively charge because it has more electrons than protons 

A molecule - when 2 or more "different" elements combine or when 2 or more of the "same" elements combine 

1 proton 1 electron < that is considered to be neutral 

3 protons, 3 electrons < neutral 

5 protons 5 electrons < neutral 

6 protons, 5 electrons <-- positive ion [more protons than electrons] 

5 protons, 8 electrons <--- negative ion [more electrons than protons] 

The answer is c) tons