If one-fourth of the radioactive sample is remaining then how many half-lives have passed? 1
2
3
4
5

Idk lolb. jinbbffv nennejejej

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.

Yes it would be a physical change.