It is common in mass spectrometry to assume that the mass of a cation is the same

Question:

It is common in mass spectrometry to assume that the mass of a cation is the same as that of its parent atom.
(a) Using data in Table 2.1, determine the number of significant figures that must be reported before the difference in mass of 1H and 1H+ is significant.
(b) What percentage of the mass of an atom 1H does the electron represent?