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)

20 percentage, you can also do it on a calculator.