.
I will give only short answers of the type "TRUE"/"FALSE".
1. FALSE.
Counter-examples:
a) Abelian groups that are direct sums of other abelian groups, are not cyclic.
b) The additive group of all real numbers is not cyclic.
c) The multiplicative group of all positive real numbers is not cyclic.
2. TRUE.
Make a proof on your own.
It is easy.
3.
4. TRUE.
If it is the function on discrete finite set, mapping it on itself.
5. FALSE.
Counter-examples:
a) Abelian groups that are direct sums of other abelian groups, are not cyclic.
b) The additive group of all real numbers is not cyclic.
c) The multiplicative group of all positive real numbers is not cyclic.
Solved, answered and explained.