Let us consider the air with the index 1 and the lucite with index 2. Using the Snell's Secound Law, we have:
Entering the unknowns, remembering that the air refrective index is 1 and the lucite refrective index is 1.5, comes:
Using the arcsin properties, we get:

Obs: Approximate results, and the drawing is attached
If you notice any mistake in my english, let me know, because i am not native.
Answer: A. It can only be motionless.
Explanation: When balanced forces act on an object, the object will not move. The only way that object can move is if the forces become unbalanced. Suppose there is a shoe on a table. You are pulling back on the shoe with a force of 3 newtons. But the friction from the shoe rubbing on the table is also 3 newtons of force. But the gravity pulling down on the shoe is also 3 newtons. Nothing will move. The only way the shoe can move is if you pulled with a little more force. The shoe would then move because the force you are pulling with is greater than the other forces acting on the shoe.
Ex 2: You are playing tug of war. Team a is pulling with 20 Newtons of force. Team b is also pulling with 20 newtons of force. The rope does not move. Team a starts to pull a little harder. Now they are pulling with 25 Newtons of force. Now the rope starts moving their way.