I'm having some issues with these, please help.?

Question

7: If the valence of element X is +2 and the valence of element Y is -3, the formula of the product when combined is
a] XY
b] X2Y3
c] X3Y2
d] X6Y6

18: The only common radical which has a positive valence is
a] SO4
b] NO3
c] NH4
d] CrO4


19: In the compound KClO3 the total negative valence is
a] -2
b] -4
c] -3
d] -6


thankyou so so much!

Answer 1

I assume when u say valence u really mean to say oxidation state or charge.

17) c +2*3 + -3*2 = 0
18) c NH4 has a +1 charge
19) d only O has a negative charge, so -2*3=-6