Answer
The student was correct in saying that $2$ is a fourth root of $16$
The student was wrong in saying that $2$ is the only fourth root of $16$ because 16 has two real roots: $2$ and $-2$.
Work Step by Step
The student was right in saying that $2$ is a fourth root of $16$
However, the student was wrong in saying that $2$ is the only fourth root of $16$.
Note that
$2^4=16 \text{ and}
\\(-2)^4=16.$
Thus, 16 has two real fourth roots: $-2$ and $2.$
