**Hint:** Apply **Snell's Law** and **Refractive index** formula to get the answer

**Snell's Law** describes the relationship between the angles of the two light waves and the indices of refraction of the two materials as**:**

**n**_{1} x **sin(q**_{1}) = n_{2} x **sin(q**_{2})

**Refractive Index (n) = D(measured)/D(apparent)**

where **D**(**measured**) is the measured depth (from the surface of the liquid to the position of the mark on the empty cell) using the microscope, and **D**(**apparent**) is the mark measurement with and without liquid.