Answer:
The minimum thickness = 83.92 nm
Step-by-step explanation:
The relation between the wavelength in a particular medium and refractive index

where ;
= wavelength of the light in vacuum
n = refractive index of medium with respect to vacuum
For one phase change :

Replacing 1.43 for n and 480 nm for λ; we have:

t = 83.92 nm
Thus; the minimum thickness = 83.92 nm