if critical angle for material of prism is C and angle of prism is A then there will be no emergent ray when
a)A2C d) A
explain the concept

This is because TOTAL INTERNAL REFRACTION OCCURS causing no emergent ray.Let max incident angle be on AB SIDE OF PRISM 90° Then r1 = C If TIR OCCUR on AC side r2 >C r1+ r2= A ) > 2CA> 2C A/2 > C.