Answer:
0.38
Explanation:
As you go from 0 % hexane (χ = 0) to 100 % hexane (χ = 1), the refractive index decreases from 1.407 to 1.375, a decrease of 0.032.
From 1.407 to 1.3948, the decrease is 0.0122 .
That is 0.0122/0.032 = 0.38 of the distance from χ = 0 to χ = 1.
The mole fraction of hexane is 0.38.
The diagram below is a plot of refractive index vs. the mole fraction of hexane. It shows that the refractive index drops to 1.3948 when χ = 0.38.
