Which of the following could not act as a medium for a mechanical wave? a) air
b) empty space
c) liquid water
d) a solid rope

b) empty space

Explanation:

A mechanical cannot travel through empty space. So option (b) is correct.

A mechanical wave is a wave which needs a material medium for its propagation. For example sound, water waves etc . The medium required by the wave can be a solid, liquid or a gas. Empty space doesn't have any medium, so a mechanical wave cannot travel through empty space.

dynamic equilibrium is the answer.

the earth would become to overheated and everything alive on it will eventually die from overheating. plants will eventually die as well, water will evaporate, and it will be nothing but a hot planet without anything living on it.