Question

Which of the following represents eighth root of x cubed in exponential form?

Answer 1

Roots take a fractional form, so the 8th root as a power is 1/8. The indices would multiply so:

x^3/8.

Answer 2

"cubed root of x squared" is "(cubed root of x) squared" = "cubed root of (x squared)" 
(x^2)^(1/3) = x^(2 * 1/3) = (x^(1/3) )^2  

So the exponent or power os 2/3.