Answer
B.
Work Step by Step
Consider the given coordinate $\left( 3,\pi \right)$ as $\left( r,\theta \right)$.
Here,
$\begin{align}
& \theta =\pi \\
& r>0 \\
\end{align}$
From above, it is clear that $\theta $ has been taken in the counter clockwise direction and
$r>0$, so $r$ lies on the terminal side.
Hence, the $\left( 3,\pi \right)$ coordinate lies on the x-axis.
