In finding out the refractive index of the glass slab, the following observations were made through a travelling microscope: 50 vernier scale divisions (VSD), 49 MSD, 20 divisions on the main scale in each cm. For the mark on paper: \[ \text{MSR} = 8.45 \, \text{cm}, \quad \text{VC} = 26 \] For the mark on paper seen through the slab: \[ \text{MSR} = 7.12 \, \text{cm}, \quad \text{VC} = 41 \] For the powder particle on the top surface of the glass slab: \[ \text{MSR} = 4.05 \, \text{cm}, \quad \text{VC} = 1 \] (MSR = Main Scale Reading, VC = Vernier Coincidence) Refractive index of the glass slab is: