Answer
See explanation.
Work Step by Step
The formula for indium oxide is $In_2O_3$, which means that for every 2 atoms of oxygen there are 3 atoms of indium.
$\frac{\text{mass of }In}{\text{mass of }O}=\frac{2M_{In}}{3M_O}$
which means:
$\frac{2M_{In}}{3\cdot 16}=4.784$
$2M_{In}=4.784\cdot 48=229.6$
$M_{In}=\frac{229.6}{2}=114.8.$
In the case of the formula $InO$ we have:
$\frac{\text{mass of }In}{\text{mass of }O}=\frac{4.784}{1.000}$
which means:
$M_{In}=4.784\cdot 16=74.5.$
Modern accepted atomic mass of indium is $114.8$.
Mendeleev’s proposed formula $In_2O_3$ gave the correct result, while the earlier formula $InO$ underestimated it badly (76.5).
