[tex]\huge \boxed{\mathcal {\gray { A nswer :}}}[/tex]
While balancing the chemical equations, the sub scripts aren't changed because by changing sub script we actually change the compound formed, hence coefficients are changed so the compound remains the same.
for example : ( for understanding )
in balancing the given reaction,
H2 + O2 =》H2O
if we change Oxygen's sub script in " H2O "
we get,
H2O + O2 =》H2O2
but here the compound formed isn't water, it is "H2O2" (hydrogen peroxide), so we can't change the sub script.
but by changing the coefficient, we get :
2 H2 + O2 =》2 H2O
