For the angle of minimum deviation of a prism to be equal to its refracting angle, the prism must be made of a material whose refractive index :
is less than 1
is greater than 2
lies between 2 and 1
lies between 2 and 2
Dm=Aμ=Sin2A2Sin A/2=2sinA/2 cosA/2sinA/2
μ2=cosA/2 If A=90o,μ=2
If A=0, μ=2
So μ lies between 2 and 2