Answer:
Hence III option is right
Step-by-step explanation:
Given that X is a random variable whose values are the number of dots that appear on the uppermost face when a fair die is rolled. The possible values of X are 1, 2, 3, 4, 5, and 6.
Let X be the reading on I dieand Y on IIdie
Both Xand Y are binomial
Given that The mean of X is 7/2 and the variance of X is 35/12.
E(X_y) =
Var(x-y) =
(Since x and y are independent covar (x,y) is 0)
i.e. 
Stddev(x-y) =
Hence III option is right