Which of the following statements about of matter is true? a. a gas has a definite volume but not a definite shape. b. a liquid does not have a definite volume or a definite shape. c. the particles in a solid tend to have less energy than those in gas. d. each substance can exist in only one state of matter.

I believe the answer is B.

idk what the options are but

these is a strong electrostatic attraction between the ions hence a lot of energy is needed to overcome this attraction

this is why the boiling points are so high

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.