Problem 23

We know from the information provided that the slant height ($l$) is 5 and the base radius ($r$) is 2.

The formula for the lateral surface area ($S$) of a cone is given by:
$$S = \pi r l$$

Substituting the given values into the formula, we get:
$$\begin{align*} S & = \pi \times r \times l \\ & = \pi \times 2 \times 5 \\ & = 10\pi \end{align*}$$

Therefore, the lateral surface area of the cone is $\boxed{10\pi}$ square units.