An isotope is one of the forms of an element that has the same number of protons, but a different number of neutrons.
A surface wave is a wave that travels along the surface of a medium. The medium is the matter through which the wave travels. Ocean waves are the best-known examples of surface waves. They travel on the surface of the water between the ocean and the air. (According to ck12.org)
So your answer would be A!
You are correct earth science is studied to predict planetery changes
Here light ray strikes to interface at an angle of 45 degree and then refracts into other medium such that it will bend towards boundary.
So here the angle of incidence will be less than the angle of refraction as light moves towards the boundary after refraction which mean it will bend away from the normal
here it can be said that medium 2 will be rarer then medium 1
So here the possible options are
1. Water
Air
2. Diamond
Air
So in above two options medium 1 is denser and medium 2 is rarer
