IMAT 2013 Q49 [Periodic Table]

The positions of the main group elements in the Periodic Table are shown below:


Which one of the following formulae is NOT correct?

A. GaCO_3
B. CsNO_3
C. BeSO_4
D. SnS_2
E. Ba(HCO_3)_2

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When looking over each compound we can see:

Gallium and a carbonate ion should not be able together in a 1:1 ratio. This is because Gallium is not able to form a 2+ ion, but rather a 3+ ion. And since we know carbonate ions have a valency of 2-, our compound should instead be:


And therefore, our answer is A.