Answer
$\text{radicand: }
y^2-8
\\\text{index: }
2$
Work Step by Step
The radicand and the index of the given expression, $
-7\sqrt{y^2-8}
,$ are
\begin{array}{l}
\text{radicand: }
y^2-8
\\\text{index: }
2
.\end{array}
In the expression $\sqrt[y] x$, y is the index while x is the radicand.