Answer:
The wavelength of the light is
.
Explanation:
Given that,
Distance between the slit centers d= 1.2 mm
Distance between constructive fringes 
Distance between fringe and screen D= 5 m
We need to calculate the wavelength
Using formula of width

Put the value into the formula




Hence, The wavelength of the light is
.
D)
Explanation:
Coz the position changes with time but the position change is not constant throughout time So, D) does not have constant velocity