1. Given data

• Density of solution $= 1.20\ \text{g mL}^{-1}$
• Molality $m = 3.30\ \text{mol kg}^{-1}$
• Molar mass of KCl $= 74.5\ \text{g mol}^{-1}$

We need to find molarity $M$ in $\text{mol L}^{-1}$.

2. Take 1 kg of solvent

Since molality is defined as moles of solute per kg of solvent,

$m = \frac{\text{moles of solute}}{\text{kg of solvent}} = 3.30$

So, for $1\ \text{kg}$ of water (solvent), moles of KCl dissolved are:

$n_{\text{KCl}} = 3.30\ \text{mol}$

3. Find mass of solute

$\text{Mass of KCl} = 3.30 \times 74.5 = 245.85\ \text{g}$

4. Find total mass of solution

Mass of solvent $= 1000\ \text{g}$

So,

$\text{Mass of solution} = 1000 + 245.85 = 1245.85\ \text{g}$

5. Convert mass of solution to volume using density

Density $= 1.20\ \text{g mL}^{-1}$

$\text{Volume of solution} = \frac{1245.85}{1.20} = 1038.21\ \text{mL}$

$= 1.03821\ \text{L}$

6. Calculate molarity

$M = \frac{\text{moles of solute}}{\text{volume of solution in L}}$

$M = \frac{3.30}{1.03821} \approx 3.18\ \text{mol L}^{-1}$

Nearest integer:

$\boxed{3}$

7. Comparison with stored answer

Derived answer = $3$

Stored correct answer = $3$

So they agree.