AP EAMCET Engineering 2018 Apr 23 Shift 2 Paper

In a unit cell of hexagonal closed packing structure, there are total six number of oxide ions per unit cell. This means there are 6 octahedral voids are present.
The number of octahedral voids occupied by ferric ions can be calculated as:

2

3

×6=4
The ratio of metal and ion is 4 : 6 = 2 : 3 .
Therefore, the correct formula of metal oxide is M2O3