Answer
Refer to the curve in Black in Graph I
Work Step by Step
For $f(x) = -\sqrt{x}$
when
$x = 9, y = -3;$
$x = 4, y = -2;$
$x = 1, y = -1;$
$x = 0, y = 0$
As seen, $f(x) = -\sqrt{x}$ is the reflection across the $x$-axis of $f(x) = \sqrt{x}$.
Domain = $[0, \infty)$
Range = $(-\infty, 0]$