The geometric mean of two surds is 1 and one of those surds is $2+\sqrt{3}$. Then the other surds is

Suppose, other surd is b.

One surd,$a=2+\sqrt{3}$

Since, by given

Geometric mean =1

$\sqrt{ab}=1$

Squaring on both sides

$ab=1$

$\begin{array}{l}b=\frac{1}{a}\\ b=\frac{1}{2+\sqrt{3}}\end{array}$

On rationalizing denominator $b=2-\sqrt{3}$