Arrange the following solutions in order of their increasing boiling points.

(i) $10^{-4} \mathrm{M} \mathrm{NaCl}$

(ii) $10^{-4} \mathrm{M}$ Urea

(iii) $10^{-3} \mathrm{M} \mathrm{NaCl}$

(iv) $10^{-2} \mathrm{M} \mathrm{NaCl}$

<h2>Step 1: Identify the van’t Hoff factor ($i$) for each solute</h2> <p><p><strong>NaCl</strong> dissociates (ideally) into two ions: </p> <p>$ \mathrm{NaCl} \;\rightarrow\; \mathrm{Na^+} + \mathrm{Cl^-}, $ </p> <p>so $i \approx 2.$</p></p> <p><p><strong>Urea ($\mathrm{CH_4N_2O}$)</strong> is a <strong>non‐electrolyte</strong> (does not dissociate), so $i = 1.$</p></p> <hr /> <h2>Step 2: Effective molar concentration of particles</h2> <p>The total particle concentration for each solution is approximately $(i \times \text{molarity})$.</p> <p><p><strong>(i) $10^{-4}\,M$ NaCl</strong> </p> <p>$ \text{Effective concentration} \;=\; 2 \times 10^{-4} = 2 \times 10^{-4}. $</p></p> <p><p><strong>(ii) $10^{-4}\,M$ Urea</strong> </p> <p>$ \text{Effective concentration} \;=\; 1 \times 10^{-4} = 1 \times 10^{-4}. $</p></p> <p><p><strong>(iii) $10^{-3}\,M$ NaCl</strong> </p> <p>$ \text{Effective concentration} \;=\; 2 \times 10^{-3} = 2 \times 10^{-3}. $</p></p> <p><p><strong>(iv) $10^{-2}\,M$ NaCl</strong> </p> <p>$ \text{Effective concentration} \;=\; 2 \times 10^{-2} = 2 \times 10^{-2}. $</p></p> <hr /> <h2>Step 3: Compare to rank the boiling points</h2> <p>A larger total particle concentration (and hence larger colligative effect) corresponds to a <strong>higher boiling point</strong>. Arrange from <strong>lowest</strong> to <strong>highest</strong>:</p> <p><p><strong>Lowest</strong>: $10^{-4}\,M$ Urea $\bigl[1 \times 10^{-4}\bigr]$ </p></p> <p><p>Next: $10^{-4}\,M$ NaCl $\bigl[2 \times 10^{-4}\bigr]$ </p></p> <p><p>Next: $10^{-3}\,M$ NaCl $\bigl[2 \times 10^{-3}\bigr]$ </p></p> <p><p><strong>Highest</strong>: $10^{-2}\,M$ NaCl $\bigl[2 \times 10^{-2}\bigr]$</p></p> <p>Hence, in the format $(\text{ii}) < (\text{i}) < (\text{iii}) < (\text{iv})$.</p> <hr /> <h2>Final Answer</h2> <p>$ \boxed{\text{(ii) } < \text{(i) } < \text{(iii) } < \text{(iv)}} \quad \text{(Option B)} $</p>