Choice C is the right answer.
Let us look at each of the choices in detail.
A. When neutral atoms (hydrogen or any other) lose an electron, the number of protons and neutrons in the nucleus still stays the same. This is the reason the ions have the same atomic mass as the neutral atom. In other words, H+ or Cl- will have the same number of protons as H and Cl, respectively. Thus, this is not the right choice.
B. The mass of a proton is 1.7 x 10^-27 kg, while that of an electron is about 9.1 x 10^-31 kg. The ratio of masses of proton and electron is about 1836. Sometimes, for simplicity, we take this ratio to be about 2000 times. Thus, this is not the right answer.
C. If the electrons were to be pulled into the nucleus of an atom by the protons, we will not see any electron at all and there would be no possibility of forming any cations or anions. This is not true (as we have cations and anions) and electrons move around the nucleus and are not pulled into it. Thus, this is the right choice.
D. Protons exist within the nucleus along with the neutrons, so this is not the answer.
Hope this helps.