Question

Describe the conditions necessary for the variance to have the value zero  

Answer 1

Variance to be zero:  only one condition that ll the values or measurements of variable must be same.

variance =  summation of  (x - a)²
             where is  x is each data value in the collection
               a is average of all data in the collection.
           Summation of squares is zero  implies that  each square is zero.
           each  x -a must be 0.

Answer 2

If all the given variables are equal it means they dont vary and thus the resultant variance is zero.