A glass $($n $=1\mathrm{.}6)$ lens is coated with a thin film $($n $=1\mathrm{.}3)$ to reduce reflection of certain incident light. If $$ is the wavelength of the light in the film, the least film thickness is

Select answer from the options below

more than $.$

$/4.$

$/2.$

less than $/4.$

$.$