<u>Answer:</u> The correct answer is Option d.
<u>Explanation:</u>
We are given:
Mass percentage of
= 20 %
So, mole fraction of
= 0.2
Mass percentage of
= 30 %
So, mole fraction of
= 0.3
Mass percentage of
= 35 %
So, mole fraction of
= 0.35
Mass percentage of
= 15 %
So, mole fraction of
= 0.15
We know that:
Molar mass of
= 16 g/mol
Molar mass of
= 28 g/mol
Molar mass of
= 26 g/mol
Molar mass of
= 48 g/mol
To calculate the average molecular mass of the mixture, we use the equation:

where,
= mole fractions of i-th species
= molar masses of i-th species
= number of observations
Putting values in above equation:


Hence, the correct answer is Option d.