similar mistake in 1(a),(b) & (c) ...
(a^n)(b^n) = (ab)^n , ... not (a+b)^n.

actually, for 1(a), (b), (c), 2(a) & (b), you should stop your working at the second last line. normally, such questions require you to "simplify" the expression. this means remove all brackets and combine whatever can be combined, so should not add back another bracket at the end.

secondly, normally, you are expected to leave answers as positive index, so for 2(d), you should write a^(-2) as a denominator of a^2.

For 2a - 2d, they are all divide questions, so for all these divisions questions the final answer must be in fraction?

it is not a matter whether they are division or or division questions. what matters is at the end, is the index clearly positive or negative.

for 2(a)(b) & (c), the index involve m, which is unknown. since cannot tell whether the index is negative, 0 or positive, you can leave the answers as you have written.

for 2(d), 'a' clearly has negative index, so we move a^(-2) to the denominator.

in general, when a variable clearly has a negative index, we make the index positive, by moving the variable from numerator to denominator, or vice versa.