Explanation:
It is given that,
Frequency of monochromatic light, 
Separation between slits, 
(a) The condition for maxima is given by :

For third maxima,



(b) For second dark fringe, n = 2





Hence, this is the required solution.
At the bottom of the rotation, the kinetic far exceeds the potential. However, at both tops, potential exceeds kinetic.