Boiling Point Elevation NEET 2025: Increasing Order for NaCl and Urea

How should you arrange 10^{-4} M NaCl, 10^{-4} M urea, 10^{-3} M NaCl and 10^{-2} M NaCl in order of increasing boiling points?

The order of increasing boiling points is (ii) < (i) < (iii) < (iv). This matches option (1) and follows directly from the effective particle concentrations.

The four solutions are (i) ${10}^{-4}$ M NaCl, (ii) ${10}^{-4}$ M urea, (iii) ${10}^{-3}$ M NaCl and (iv) ${10}^{-2}$ M NaCl. The task is to arrange these in order of increasing boiling points. The four ordering choices are:

What does the official NEET solution show for this boiling point elevation calculation?

ΔTb is proportional to i × C for dilute aqueous solutions. The official solution assigns i = 2 for each NaCl (dissociates into two ions) and i = 1 for urea (non-dissociating). This produces i × C values of $2\times {10}^{-4}$, $1\times {10}^{-4}$, $2\times {10}^{-3}$ and $2\times {10}^{-2}$.

For (i) ${10}^{-4}$ M NaCl: $i\times C=2\times {10}^{-4}$

For (ii) ${10}^{-4}$ M urea: $i\times C=1\times {10}^{-4}$

For (iii) ${10}^{-3}$ M NaCl: $i\times C=2\times {10}^{-3}$

For (iv) ${10}^{-2}$ M NaCl: $i\times C=2\times {10}^{-2}$

Direct numerical comparison yields (ii) < (i) < (iii) < (iv), matching option (1). The values differ by exact factors of 2 and 10.

What exact method mistake produces the wrong option in this boiling point elevation NEET 2025 question?

Using raw molarity C for all four solutions without multiplying by i for the NaCl solutions produces the wrong order. This yields 10^{-4}, 10^{-4}, 10^{-3} and 10^{-2}, which collapses (ii) and (i) or approximates (i) with (iii) by ignoring the doubling of particles.

The correct method requires i = 2 for every NaCl irrespective of the given concentration because all are dilute. Dissociation is complete at these levels, so the multiplier applies uniformly.

What related practice questions from the solutions chapter build the same skill?

Question 1: Arrange 0.1 m glucose, 0.1 m NaCl and 0.05 m CaCl2 in increasing order of freezing point depression.

Freezing point depression follows the same i × m rule. Glucose has i = 1, NaCl has i = 2 and CaCl2 has i = 3. The effective values are 0.1, 0.2 and 0.15. The order of increasing depression is glucose < CaCl2 < NaCl.

Question 2: Compare osmotic pressures at the same temperature for 0.01 M urea, 0.01 M NaCl and 0.005 M AlCl3.

Osmotic pressure is proportional to i × C. Urea has i = 1 (effective 0.01). NaCl has i = 2 (effective 0.02). AlCl3 has i = 4 (effective 0.02). The order is urea < NaCl ≈ AlCl3.

To find more PYQs like these from previous years, search the past-paper archive by chapter.

Why does i × C decide the order every time in boiling point elevation NEET 2025 questions?

Colligative properties depend only on total number of solute particles, not their identity. The effective concentrations here are ${10}^{-4}$, $2\times {10}^{-4}$, $2\times {10}^{-3}$ and $2\times {10}^{-2}$. These differ by factors of 2 and 10.

Molarity can be used directly in place of molality for these dilute levels (difference < 0.1 %). Once the four i × C numbers are written, sorting takes seconds.

What 60-second routine solves any similar ordering question in NEET 2025 Chemistry?

Step 1: assign i (1 for non-electrolytes, 2 for NaCl, 3 for MgCl2 etc.).

Step 2: multiply i by given C or m and write the four numbers.

Step 3: sort the numbers and map back to labels; never compare concentrations directly.

This routine keeps the question type at 120 seconds or less when i values are memorised. Practise it on the two questions above until the pattern feels automatic. If a similar question still confuses you during practice, photograph a doubt for a step-by-step solution.

Next step: the past-paper archive on NEET JEEnius AI and search past NEET papers by year, subject or chapter, each with a worked solution (100 free searches a month).

Keep going with Atoms and Nuclei NEET 2025: De Broglie Wavelength Ratio in Bohr Model.