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.