The of a radical expression is the number indicating which root (square root, cube root, etc.) is meant.

The index depicts which root is meant. Thus, for example, if we mean the cube root of some number, say , it is shown as . Likewise, fourth root of is shown as . So on and so forth this continues. The only exception to this rule is the square root, wherein, by convention, we do not write the index and still it is understood that it is the second root that is meant.

Thus, the correct answer is "index".

Therefore, The index of a radical expression is the number indicating which root (square root, cube root, etc.) is meant.

where is the option given