Answer:
third choice in image. √(16³)
the squareroot of 16 to the third power
Explanation:
Fractional exponents tell you that you have roots. Could be squareroot or thirdroot, fourth root, fifth root...etc. You know which because you look at the bottom number (denominator) of the fraction. I use the phrase "down and out" to help remember that the bottom number in the fractional exponent is the "outside number" (index) on the radical sign.
The top number (numerator) of the fraction is an exponent. It can be either inside the radical right there on the shoulder of the 16 or it could also be outside the whole entire radical.
16^ (3/2) = √(16³) = (√16)³