A Young's double slit experiment is done in air and the same set up is immersed in a liquid of refractive index $\mu$. It is found that the 10th bright fringe in liquid was in the same position as 6th dark fringe in air . The value of $\mu$ is

Question

$(a)\;1.52 \\ (b)\;1.8 \\ (c)\;1.65 \\ (d)\;1.5 $