Monochromatic Light of Wavelength $\lambda$ _film Is Normally Incident on a Soap Film in Air

Multiple Choice

Monochromatic light of wavelength $\lambda$ _film is normally incident on a soap film in air. In terms of the wavelength, what is the thickness of the thinnest film for which the intensity of the reflected light will be a maximum?

A) $\lambda$ _film/4
B) $\lambda$ _film/2
C) 3 $\lambda$ _film/4
D) $\lambda$ _film
E) 3 $\lambda$ _film/2