This question tests your knowledge of the behaviour of light through different mediums. We know that when light travels from air through glass, it tends towards the normal. This is because the glass is denser than air ie: n(glass)>n(air). Our glass blocks increase in density infinitely, so, applying our knowledge from earlier, we can say that the light will tend towards the normal until the infinitieth block where its path is on the normal, so the angle to the normal is 0 degrees.