#### Answer

Rationalizing a denominator means you rewrite a radical expression so that there is no radical in its denominator.
Refer to the expanation and illustration below.

#### Work Step by Step

Rationalizing a denominator means you rewrite a radical expression so that there is no radical in its denominator.
This can be done by multiplying a radical expression to both the numerator and the denominator so that the radical in the denominator becomes a perfect square.
To simplify $\dfrac{2}{\sqrt5}$, multiply $\sqrt5$ to both the numerator and the denominator as it will make the denominator become $\sqrt{25}$, which is equal to $5$.
To illustrate:
\begin{align*}
\frac{2}{\sqrt5}&=\frac{2}{\sqrt5} \cdot \frac{\sqrt5}{\sqrt5}\\\\
&=\frac{2\sqrt5}{\sqrt{25}}\\\\
&=\frac{2\sqrt5}{5}
\end{align*}