In a young's double slit experiment illuminated by monochromatic light the slit separation is $0.3\;mm$ and slit- screen separation is $1.5 \;m$. If fourth bright fringe is 1 cm from central bright fringe, the wavelength of light used is

Question

$(a)\;4000\;A^{\circ} \\ (b)\;5000\;A^{\circ} \\ (c)\;3000\;A^{\circ} \\ (d)\;1000\;A^{\circ} $