Light of Wavelength 500 Nm Illuminates a Soap Film

Multiple Choice

Light of wavelength 500 nm illuminates a soap film ( n = 1.33) . What is the minimum thickness of film that will give an interference when the light is incident normally on it?

A) 24 nm
B) 56 nm
C) 94 nm
D) 188 nm
E) 376 nm