In Young's double slit experiment, the wavelength of red light is `5200 Å`. The value of n for which nth bright band due to red light coincides with `(n+1)th` bright band due to blue light, is

Explanation

`(n_(R)lambda_(R)D)/(d) = (n_(B)lambda_(B)D)/(d)` or `(n_(R))/(n_(B))= (lambda_(B))/(lambda_(R))= (5200)/(7800) =(2)/(3)`
Therefore `2^(nd)` of red coincides with `3^(rd)` of blue.