Hope it helped you.
A. Acceleration is a wrong answer. Acceleration is the rate of change to in velocity. It involves a change in speed and direction.
B. Force is a wrong answer. Force is a directions from push/or pull.
C. Inertia is a correct. Inertia is a tendency of an object to stay at the rest or preserve its state of motion.
D. Velocity is a incorrect answer. Velocity is the placement of an object during a specific unit of time. It has two measurements are needed to determine velocity.
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Answer:
(a) 
(b) 
(c)
(d)
Solution:
As per the question:
Refractive index of medium 1, 
Angle of refraction for medium 1, 
Angle of refraction for medium 2, 
Now,
(a) The expression for the refractive index of medium 2 is given by using Snell's law:

where
= Refractive Index of medium 2
Now,

(b) The refractive index of medium 2 can be calculated by using the expression in part (a) as:


(c) To calculate the velocity of light in medium 1:
We know that:
Thus for medium 1
(d) To calculate the velocity of light in medium 2:
For medium 2:
you would multiply 30 by 15. because its the weight times the distance.