I have the answers to these questions already, I just want to make sure that I haven't forgotten anything and I have my facts straight.

Q1):
what kind of pattern of light would you get if you shone monochromatic light on a diffraction grating? What pattern of light would you get if you shone white light on a diffraction grating?

A1):
When monochromatic light is shone through diffraction grating a pattern of interference fringes forms.
When white light passes through diffraction grating the light is separated into its constituent colors.

Q2):
Is is correct to say that the difference in the patterns produced by monochromatic and white light is caused by the fact that monochromatic light waves interfere with each other when the pass through a diffraction grating, while the rays of white light do not? Explain.

A2):
It is an incorrect statement. Both patterns are produced by interference despite their different manifestations. When white light passes through diffraction grating the bright fringe of one wavelength fills in the dark fringe of another frequencies dark fringe. Monochromatic light has no other wavelength to fill its dark fringes, resulting in a visible pattern.

Q3):
Goggles hold air around a person's eye when he or she swims underwater. One person wearing goggles and one person with out goggles are standing at the side of a pool. Both see a coin on the bottom of the pool, and both jump in to retrieve it. when they are underwater, the person without goggles sees the coin at a greater depth than it was when he was above the water. The person with goggles sees the coin at exactly the same depth as it was when she was on the pool side. Which of the two sees the coin at its actual depth? Explain the reason for your answer.

A3):
When underwater, light travels in straight lines, however when wearing goggles air is introduced. When a ray of light enters or exits the water, because of the change of medium,it bends thus distorting the image.
Therefore the person not wearing goggles is seeing the coin at its true depth.

Thank you!