When balancing a chemical equation which of the following is true?
a) subscripts cannot be changed.
b)coefficients cannot be changed.
c)the number of atoms can be changed.
d)subscripts and coefficients can both be changed.

Both models are effective because they show the valence electrons, and these valence electrons indicate the reactivity of an element.

It is a body of knowledge gained  using  inquiry and experimentation 

Sorry im just trying to get answers like you are 

2poclâ‚(g) ⇜ 2 pclâ‚(g) + oâ‚‚(g) â†gâ° = (2 mol)î”gfâ°(pclâ‚) – (2 mol)î”gfâ°(poclâ‚) = (2 mol)(–270 –(–502) kj/mol) â†gâ° = + 464 kj = â†hⰠ– tî”sâ° î”sâ° = 179 j/k ⇒ â†hâ° = â†gâ° + (298 k)(179 j/k) = –411 kj assuming that î”hâ° and î”sâ° do not depend on temperature, the temperature at which â†gâ° = 0 is where t = â†hâ°/î”sâ° = (–411 kj)/(0.179 j/k) = 2294 k. at that temp. keq = 1 for the reaction.