Hydrogen is the limiting reactant because when doing a stoichiometry equation for the reactants, hydrogen will be used completely by having a smaller yield and oxygen will be excess (7 moles to be exact)
Nickle (II) sulfite - b/c the charge on Ni can be +2 or +3 i Believe. SO3 has a charge of -2 the you need nickel II (+2) to make a proper ionic bond