Question

the refractive index of Glass with respect to where is 2 then the critical angle of glass air interface is

Answer 1

refractive index =1÷sinC
2=1÷sinc
sinc=1÷2
c=30degrees

Answer 2

For critical angle , the raay will go from glass to air.

By snell's law  

µgsinc = µasin90

or  

sinc=µa.1/µg

according to question µg/µa =2

then  

sinc = 1/2

c=sin^-1(1/2)

angle c =30°