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Arrange the following solutions in order of their increasing boiling points. (i) 10^-4 M NaCl (ii) 10^-4 M Urea (iii) 10^-3 M NaCl (iv) 10^-2 M NaCl

1. (i) < (ii) < (iii) < (iv)
2. (ii) < (i) ≡ (iii) < (iv)
3. (i) < (ii) < (iv) < (iii)
4. (iv) > (iii) > (i) > (ii)

Correct answer: (i) < (ii) < (iii) < (iv)

Solution

The boiling point elevation is determined by the number of solute particles in solution. Since NaCl dissociates into two ions (Na+ and Cl-) while urea does not dissociate, the 10^-4 M NaCl solution has a higher effective concentration of particles than the 10^-4 M urea solution. Therefore, as the concentration of NaCl increases, the boiling point also increases, leading to the order of (i) < (ii) < (iii) < (iv).

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