A sample experiment revealed that PVC formed in the medium has $\left(M_{n}\right)=13$, and $\left(M_{w}\right)=16$, where $\left(M_{n}\right)$ stands for the number average molar mass and $\left(M_{w}\right)$ for the weight average molar mass. The variance of $M_{n}$ will then be
(a)39
(b)3
(c)1
(d)87
Answer
Answer (as printed): A
Explanation
Variance = (difference between weight-average and number-average molar mass) $\times$ molar mass = $(16-13)\times13 = 3\times13 = 39$.Here molar mass represented $x_i$ and weighted molar mass $f_i$.