The correct answer is B) One atom of calcium and two atoms of chlorine. I just had the same question on my 9th grade science test today. I hope I didn't give the answer to you too late and I hope it helps you out
Answer: The 5 uses of mechanical energy are: 1) Hammering a nail
2) Using Dart gun 3) Moon 4) Hydropower plant 5) Sharping a pencil.
The one that's completely submerged is displacing more water, so the buoyant force on it is greater.