(i) Sample A has more protons than the electrons.
Hence, it is a cation.
(ii) Sample B and C have same mass number (Mass number = Number of protons + number of
neutrons = 37) but different atomic numbers
(i.e. 18 and 17 respectively). Hence, they are a pair of isobars.
(iii) Samples C and D have same atomic number but different mass numbers. Hence, they are a pair of isotopes.