This is still subject to review, but apparently a GP with r=0 cannot exist to form a limiting sum of 2, as a=2 for that to occur. Thus your series is 2+0+0+0+0,..... Term2/Term1=0/2=0 but Term3/Term2=0/0=undefined. So a GP must have a non-zero common ration, if 'a' is a non-zero number. Which means the answer may be 0<a<4, a is not equal to 2 (when r=0). Pretty sure this question was designed to trick the state though, so I'm not sure how they'll receive it in the marking center. But it is 3 marks, so other than rearrange the question or graphing/determining the range for 2 marks, the other one is likely gained by recognizing the restriction.

The only case where a zero GP may exist is when 'a'=0 i.e. 0,0,0,0,... which doesn't provide a limiting sum of 2.