<u>Answer:</u> The percentage by mass of NaCl in the mixture is 38.5 %
<u>Explanation:</u>
To calculate the mass percentage of element in compound, we use the equation:
.......(1)
Mass of sodium element = 23 g
Mass of NaCl = 58.5 g
Putting values in equation 1, we get:

Mass fraction of sodium metal in NaCl = 0.3932
- <u>For
:</u>
Mass of sodium element = 23 g
Mass of
= 85 g
Putting values in equation 1, we get:

Mass fraction of sodium metal in sodium nitrate = 0.271
Let us assume the mass fraction of NaCl in the mixture is 'x'
So, the mass fraction of
in the mixture will be '(1-x)'
We are given:
Percent by mass of Na in the mixture = 31.8 %
Mass fraction of Na in the mixture = 0.318
Evaluating the mass fraction of NaCl in the mixture:
![[(x\times 0.3932)+((1-x)\times 0.271)]=0.318](https://tex.z-dn.net/?f=%5B%28x%5Ctimes%200.3932%29%2B%28%281-x%29%5Ctimes%200.271%29%5D%3D0.318)
x = 0.385
Percent by mass of NaCl in the mixture will be = 
Hence, the percentage by mass of NaCl in the mixture is 38.5 %