Wave Optics Questions

The Brewsters angle $i_b$ for an interface should be:

In Young’s double slit experiment, if the separation between coherent sources is halved and the distance of the screen from the coherent sources is doubled, then the fringe width becomes:

Assume that light of wavelength $600\text{nm}$ is coming from a star. The limit of resolution of telescope whose objective has a diameter of $2\text{m}$ is: