In the figure shown in a YDSE, a parallel beam of light is incident on the slits from a medium of refractive index \[{{n}_{1}}\].The wavelength of light in this medium is\[{{\lambda }_{1}}\]. A transparent slab of thickness t and refractive index is put in front of one slit. The medium between the screen and the plane of the slits is \[{{n}_{2}}\]. The phase difference between the light waves reaching point O (symmetrical, relative to the slit) is

• A. \[\frac{2\pi }{{{n}_{1}}{{\lambda }_{1}}}({{n}_{3}}-{{n}_{2}})t\]
• B. \[\frac{2\pi }{{{\lambda }_{1}}}({{n}_{3}}-{{n}_{2}})t\]
• C. \[\frac{2\pi {{n}_{1}}}{{{n}_{2}}{{\lambda }_{1}}}\left( \frac{{{n}_{3}}}{{{n}_{2}}}-1 \right)t\]
• D. \[\frac{2\pi {{n}_{1}}}{{{\lambda }_{1}}}({{n}_{3}}-{{n}_{2}})t\]