You observe a light ray move from one piece of glass to another (a different type of glass) and the light ray bends towards the glass-glass interface (away from the normal) when it enters the 2nd piece of glass. you deduce that:

second medium is less optical denser than first medium

Explanation:

As per Snell's law we know that

so here we know that

= angle of incidence

= angle of refraction

As we know that light ray goes away from the normal when it move from medium 1 to medium 2

so here angle of refraction will me more than the angle of incidence

so we have

since we know that

so we have

so we can say that

so we can say that second medium is less optical denser than first medium