Explain why particles of a colloidal solution do not settle down when left undisturbed, while in the case of suspension they do.

The teacher instructed three students $\text{'}\mathrm{A}, \text{'}\mathrm{B}\text{'}$ and $\text{'}\mathrm{C}\text{'}$ respectively to prepare a $50\%$ (mass by volume) solution of sodium hydroxide $\left(\mathrm{NaOH}\right)$. $\text{'}\mathrm{A}\text{'}$ dissolved $50 g$ of $\mathrm{NaOH}$ in $100\mathrm{mL}$ of water, $\text{'}\mathrm{B}\text{'}$ dissolved $50\mathrm{g}$ of $\mathrm{NaOH}$ in $100 g$ of water while $\text{'}\mathrm{C}\text{'}$ dissolved $50\mathrm{g}$ of $\mathrm{NaOH}$ in water to make $100\mathrm{mL}$ of solution. Which one of them has made the desired solution and why?