Question

A gaseous mixture contains four gases $A,B,C$ and $D$. The mole fraction of $B$ is 0.5. the mole fraction of $A$ is:

• A. 0.525
• B. 0.375
• C. 0.625
• D. 0.732

Answer 1

The correct option is B 0.375

Let the mole fraction of $A$ be denoted by $X_a$

Let the mole fraction of $B$ be denoted by $X_b$= 0.5 (given)

Let the mole fraction of $C$ be denoted by $X_c$

Let the mole fraction of $D$ be denoted by $X_d$

Since $A$,$B$,$C$,$D$ are all present together,

$X_a$+$X_b$+$X_c$+$X_d$= $1$

$X_a$ + $X_c$ +$X_d$ = $1$- $X_b$= $1 - 0.5 = $0.5$

Thus $X_a$ must be less than $0.5$

According to the options given in the question only $0.375$ is less than $0.5$

Thus Mole fraction of $A$= $0.375$