In a Young's double slit experiment separation between two consecutive dark. fringes is $1.2 \;mm$, wave length $\lambda$ of light is $600 \;nm$ Distance between source and screen $D= 1 m$, the separation between slits is

Question

$(a)\;1\;mm \\ (b)\;0.05\;mm \\ (c)\;0.5 \;mm \\ (d)0.1 \;mm$