A plate of refractive index 1.6 is introduced in the path of light from one of the slits in Young's double slit experiment then

When a thin plate of refractive index \(n\) is introduced in front of one of the slits in Young's double-slit experiment, it adds an extra optical path (and hence a phase difference) to the light coming from that slit. This shifts the entire interference pattern on the screen but does not change the fringe spacing or make the pattern disappear.
Fringe width does not change because it depends on the slit separation and the wavelength in air, not on a uniform phase shift introduced in one path.
Number of visible fringes does not necessarily decrease (as long as the plate is not too thick to cause excessive absorption or other effects).
The interference pattern does not vanish unless coherence is destroyed (e.g., by scattering or large thickness variations).
The net effect of introducing a uniform optical path difference in one slit is a lateral shift of the central maximum (and all fringes) toward the slit with the plate.
Hence the correct statement is :
(B) The central maximum will shift towards the side on which the plate is introduced.