#### Answer

not a real number

#### Work Step by Step

The given expression, $
\sqrt{25-144}
,$ simplifies to
\begin{array}{l}\require{cancel}
\sqrt{-119}
.\end{array}
Since the index of the given expression, $
\sqrt{-119}
,$ is even (index = $
2
$) and the radicand is negative (radicand = $
-119
$), then the given expression is $\text{
not a real number
.}$