The equation 2 n o 2 in equilibrium with n 2 o 4 represents a system, a. in physical equilibrium b. in chemical equilibrium c. that goes to completion d. that does not change

i believe it is-

d.) gravity pulled particles of dust and gas together to form planets.

i don't see a text, but i am gonna assume this *orbit* the curved path, usually elliptical, described by a planet, satellite, spaceship, etc., around a celestial body, as the sun.