A ray of light travels from air to water to glass and again from glass to air. Refractive index of water with respect to air is 'x', glass with respect to water is 'y' and air with respect to glass is 'z'. Which one of the following is correct?

When the distance of separation between the slit and screen is doubled, the angular separation between fringes in single slit diffraction pattern experiment

Light of wavelength $\lambda$ is incident on a single slit of width 'a' and the distance between slit and screen is D. In diffraction pattern, if slit width is equal to the width of the central maximum then D is equal to

Light of wavelength '$\lambda$' which is less than threshold wavelength is incident on a photosensitive material. If incident wavelength is decreased so that emitted photoelectrons are moving with some velocity then stopping potential