Write the formulas of the compounds formed by NH4 with the following anions: NO3−, ClO3−, SO42−, HPO42−

a) NH4NO3, NH4ClO3, NH4SO4, NH4HPO4
b) NH4NO2, NH4ClO2, NH4SO3, NH4HPO3
c) NH4NO4, NH4ClO4, NH4SO5, NH4HPO5
d) NH4NO5, NH4ClO5, NH4SO6, NH4HPO6