Help understanding step $3.$ Can someone explain why I can't use Alternative step $3$ instead of $3$ since we have mass of ZnS produced. And why step $3$ uses Zn$\text{'}$s exten of reaction?

Question: Calculate the theoretical yield of zinc sulphide, in grams, from the reaction of $0\mathrm{.}5g$ zinc and $0\mathrm{.}5g$ sulphur. If the actual yield is $0\mathrm{.}6gZnS,$ what is the percentage yield?

$8Zn+S_{8}8ZnS$

$=$ extent of raction

$=\frac{n}{v}=\frac{m}{Mv}$

step $1$:

$Z_n=\frac{0\mathrm{.}5(g)}{65\mathrm{.}38\frac{g}{m}ol8}=9\mathrm{.}56{10}^{-4}$mol

Step $2$:

$S_8=\frac{0\mathrm{.}5(g)}{256\mathrm{.}48\frac{g}{m}ol1}=1\mathrm{.}95{10}^{-3}$mol

Step $3$: $Z_{n}S$

$n=v=9\mathrm{.}56{10}^{-4}$mol$c=7\mathrm{.}65{10}^{-3}$mol

Alternative step $3$

$Z_n=\frac{0\mathrm{.}68}{97\mathrm{.}474\frac{g}{m}ol}$