Europium can have 2+ or a 3+ charge which one of these formulas is not possible

1) EuSO4
2)Eu2(SO4)3
3)EuPO4
4)Eu(NO3)3
5) EuHCO3

In compunds where M is +2 and A(anion) is -2 the correct formula is MA.

For compounds in which M is +3 and A is -2, the formula is M2A3.
You note here that the valence (in your case the charge) of M is the subscript for A and the valence of A is the subscript for M. In taking this shortcut, the only thing you need to watch for is that if it comes out M2A2 pr M3A3 you should use the lowest numbers; i.e., MA. So 1 is possible, 2 is possible, etc. I'll leave the others to you.