Also how many atoms are in 4Mg3P2, so how many magnesium atoms and P atoms

Spontaneity tell us the direction of the reaction, but not how fast it goes. gibbs free energy brings together enthalpy, entropy and temperature in one easy formula. g = h - ts. and, finally the sign of delta g is always negative for a spontaneous reaction.

I'm pretty sure its c

There are two molecules. check the attached file for the solution.

The chlorine is the chemical property