Answer
See work below.
Work Step by Step
a) $Na_{2}$$SO_{4}$ : sodium sulphate (group IA only forms 1+ cations)
b) $Na_{3}$$N_{1}$ : sodium nitride (group IIA only forms 1+ cations)
c) CuCl: copper(I)chloride (group IB form 1+ and 2+ cations)
d) $Cr_{2}$$O_{3}$ : chromium(III)oxide (group VIB forms numerous oxidation states)