1) True
2) If you consider that a+b can be equal to c, then, (a+b)^2 = c^2.
c^2 is in exponential form. Hence, the given statement is true.
3) (ab)^3 = a^3*b^3. The given statement is false.
4) Take into account that the number (-5)^10 is positive regardless the base is 5 or -5 (becasue the exponent is odd, then, the result is always positive). Then,
(-5)^10 can be written also as (5)^10 and the given statement is true.
5) By definition, a term written in the form x, y or a, has exponent 1. The statement is true.