Efficency of a lever is always less than hundred percent. why?​

According to social exchange theory, altruistic behaviors benefit the individual who performs them. t/f

If it takes a planet 2.8 x 10^8 s to orbit a star with a mass of 6.2 x 10^30 kg what is the average distance between the planet and the star

At very high pressures, gases become and will eventually a) more dense; become hotter b) more dense; change to a liquid or solid c) less dense; combust d) less dense; turn into a liquid