$A$ sample of ferrous oxide has actual formula $Fe_{0.93}O_{1.00}$. In this sample,what fraction of metal ions are $Fe^{2+}$ ions? What type of non-stoichiometric defect is present in this sample?

(N/A) Let the number of $O^{2-}$ ions $= 100$.
Then,the number of $Fe$ ions $= 93$.
Let the number of $Fe^{2+}$ ions $= x$.
Then,the number of $Fe^{3+}$ ions $= (93 - x)$.
Since the compound is electrically neutral,the total positive charge must equal the total negative charge:
$2x + 3(93 - x) = 2 \times 100$
$2x + 279 - 3x = 200$
$-x = 200 - 279$
$x = 79$.
Thus,the number of $Fe^{2+}$ ions is $79$.
The fraction of $Fe^{2+}$ ions $= \frac{79}{93} \approx 0.849$.
The sample exhibits a metal deficiency defect because the number of $Fe$ ions is less than the number required for the stoichiometric ratio $(1:1)$.