Question

Formula of nickel oxide with metal deficiency defect in its crystal is $A_{0.8}O$. The crystal contains $A^{2+}$ and $A^{3+}$ ions. The fraction of nickel existing as $A^{2+}$ ions in the crystal is

• A. 0.96
• B. 0.04
• C. 0.50
• D. 0.31

Answer 1

Answer: (C)

So the ratio of $A:O=80:100$
Thus, if there are 100 atoms of oxygen then 80 atoms of $A$.
Let $x$ be the no. of atoms of $A^{+2}$.
No. of atoms of $A^{+3}=80-x$
Charge on A = Charge on O
Since oxygen has charge $-2$.
Therefore,
$<br/>\begin{array}{l}<br/>2x+3(80-x)=2\times 100\\ <br/>2x+240-3x=200\\ <br/>\Rightarrow x=40<br/>\end{array}<br/>$
Therefore,
Fraction of $A^{+2}=\frac{\text{ Atoms of }{A}^{+2}}{\text{ Total no. of atoms }}$
$\Rightarrow$ Fraction of $A^{+2}=\frac{40}{80}=0.50$