Light will refract or bend as it crosses the boundary between two materials. The direction that it bends - either towards the normal line or away from it - depends upon the relative speed of the light in the two media. Since the speed of light is dependent upon the index of refraction of the material, the direction of bending also depends on the relative index of refraction.
 

The Underlying Principle

When the relative speed of light in the two media are known, the direction that light bends can be easily predicted. The direction is typically expressed as being towards the normal  or away from the normal. The normal refers to the normal line drawn perpendicular to the boundary at the point of contact of the incident ray. The rules are ...

1. FST Rule: When light passes from a material in which it is traveling Fast into a material in which it travels Slower, it will bend Towards the normal.
2. SFA Rule: When light passes from a material in which it is traveling Slow into a material in which it travels Faster, it will bend Away from the normal.

Just think of FST and SFA to remember the rules. If that doesn't help, we usually suggest Freaky Science Teachers and Somebody Farts Alot (or substitute your favorite S name for Somebody, like Suzie of Stephen or Sammy, etc.).

 

Relating Index of Refraction to Speed

So the rule for the direction of bending as expressed above is speed based. But this question provides information about the relative index of refraction (n) of the two materials. So part of the challenge of this question is to relate the index of refraction to the speed of light. The rule is quite simple - light travels fastest in the material that has the smallest index of refraction (n) value. So the information about the relative n values can be transformed into speed infomation. For instance, if n₁ > n₂, then light travels faster in medium 2 than in medium 1. And similarly, if n₂ > n₁, then light travels faster in medium 1 than in medium 2. 

 

Know Your Boundary ... Know What's Normal.

The given diagrams show material 1 and material 2 separated by a line. The line is the boundary. A boundary is simply the separation line between two different materials. The light bends at this boundary. A boundary can be vertical, horizontal, and even angled to the vertical and horizontal. You will just have to look at each diagram individually and determine the boundary. Be careful. Be observant. 

But there's more to it than that. You need to know where the normal line is. It is not drawn. You have to visualize it. If visualizing things is difficult, then just hold a ruler or pencil up on the screen to represent the normal line. The normal line is the imaginary line that is drawn perpendicular to the boundary. So if the boundary is horizontal, then the normal line is vertical. And if the boundary is vertical, the normal line is horizontal. The bending that takes place is described as being towards the normal or away from the normal. So you really need to be able to identify the normal line.


 

Towards Versus Away

Many students know the above FST and SFA rules; they just don't know what towards the normal and away from the normal looks like. It's probably the most difficult part. When the light ray is said to refract towards the normal, we mean that the refracted ray is positioned closer to the normal line than the incident ray is. Put another way, the angle of refraction (measured relative to the normal line) is smaller than the angle of incidence in a towards the normal refraction situation. 

And when we say that the light ray refracts away from the normal, we mean that the refracted ray is positioned further away from the normal line than the incident ray is. Put another way, the angle of refraction (measured relative to the normal line) is larger than the angle of incidence in an away from the normal refraction situation. The diagram below depicts these two contrasting situations.