1. Relate van’t Hoff factor to degree of dissociation

For the salt $\mathrm{MX_3}$:

$\mathrm{MX_3 \rightarrow M^{3+} + 3X^-}$

So, one formula unit gives a total of $4$ particles after complete dissociation.

2. Use the general formula for van’t Hoff factor

If $\alpha$ is the degree of dissociation, then for a solute producing $\nu$ particles,

$i = 1 + (\nu - 1)\alpha$

Here, $\nu = 4$, so

$i = 1 + (4-1)\alpha = 1 + 3\alpha$

3. Substitute the given value

Given:

$i = 2$

Hence,

$2 = 1 + 3\alpha$

$3\alpha = 1$

$\alpha = \frac{1}{3}$

4. Convert to percentage dissociation

$\%\text{ dissociation} = \alpha \times 100 = \frac{1}{3}\times 100 = 33.33\%$

Nearest integer:

$\boxed{33}$

5. Comparison with stored answer

Stored correct answer = $33$

Our derived answer = $33$

So they agree.