If `n_(v),n_(r),n_(b)` are the refractive indices of violet, red and blue light respectively, in a given medium then which of the following is true ?
A. `n_(v)=n_(b)=n_(r)`
B. `n_(v) gt n_(b) gt n_(r)`
C. `n_(v) gt n_(b) lt n_(r)`
D. `n_(v) gt n_(r) gt n_(b)`