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What you can't understand in the above ques?Simply apply the properties and you'll reach your answer for sure. For a group to be abelian it has gotta follow commutative property. Also note that in a few cases such as that of class of natural numbers,real numbers,rational numbers,integers there are certain cases of addition and multiplication which do not hold while they hold in other cases. Simply apply the properties of abelian group.

Answer 1

G is group, it is given data

now (ab)$^{-1}$=a$^{-1}$b$^{-1}$

in general (ab)$^{-1}$=b$^{-1}$a$^{-1}$

so b$^{-1}$a$^{-1}$=a$^{-1}$b$^{-1}$

ab=ba

Group + commutative properly is nothing but abelian group