1. Plasma is "the state..." because plasma is rarely natural on earth (only lightning strikes) and has the highest temp
gas is "particles move freely" they do move freely
liquid is "it expands to fill volume" they do not have definite boundaries so they fill up the container
solid is "it retains its shape" yup dis is pretty obvious ig
2.
I agree with your answers.
it wouldnt be hypothesis or theory because they are basically the same thing and they explain facts. fact would be the best answer
conduct experiments would be the most logical here because you can gain new knowledge from conducting experiments instead of the rest.