Which of the following represents eighth root of x to the fifth power in exponential form?

First note that the nth root of a number, a, is a^ (1/n).

So you have:

(x^5) ^ (1/8)

Next note that (a^b) ^c=a^ (bc) so you have:

x^ (5 (1/8))

x^ (5/8) or if you'd rather have a decimal ...

x^ (0.625)