Question

Liquid M and liquid N form an ideal solution. The vapour
pressures of pure liquids M and N are 450 and 700 mmHg,
respectively, at the same temperature. Then correct statement
is:
$x_M$ = mole fraction of M in solution;
$x_N$ = mole fraction of N in solution;
$y_M$ = mole fraction of M in vapour phase;
$y_N$ = mole fraction of N in vapour phase

• A. $\frac{x_M}{x_N}>\frac{y_M}{y_N}$
• B. $(x_M-y_M)<(x_N-y_N)$
• C. $\frac{x_M}{x_N}<\frac{y_M}{y_N}$
• D. $\frac{x_M}{x_N}=\frac{y_M}{y_N}$

Answer 1

The correct option is A $\frac{x_M}{x_N}>\frac{y_M}{y_N}$

Liquid M and N form an ideal solution. Vapour pressures of
pure liquids M and N are 450 and 700 mm Hg respectively.
$\therefore p^{o}N>p^{o}M$
So, by using Raoult’s law
$y_N>x_N...\left(i\right)$
$x_M>y_M...\left(ii\right)$
Multiplying (i) and (ii) we get
$y_N{x}_M>y_M{x}_N$
$\frac{x_M}{x_N}>\frac{y_M}{y_N}$