Small critical angle = high refractive index

The smaller the critical angle of a material, the higher its refractive index will be.

Small critical angle $rArr$ High refractive index

Water to air

Critical angle $~~50^circ$ $n=1.3$

Critical angle of light travelling from water to air.

Critical angle $~~42^circ$ $n=1.5$

Critical angle of light travelling from glass to air.

Critical angle $~~24^circ$ $n=2.4$

Critical angle of light travelling from diamond to air.

$Refractive index and critical angle of water glass and diamond.$

NOTE: Low refractive number gives low density and large critical angle.

High refractive number gives high density and small critical angle.