Ionic substance AB crystallises in rock salt structure. If all ions at the centre of the faces and at the body centre are removed, what should be the percentage of number of ions remained?

Explanation

Say `B^(-)`ions are present at the 8 corners and at the 6 face centres. At ions are present at the 12 face edges and at the centre of the body.
` B^(-)` ions originally present =`(8 xx(1)/(8)) +(6 xx (1)/(2)) = 1 +3`
`A^+` ions originally present `= (12 xx 1/4 )+ (1xx 1) = 3+1 `
. `B^-` ions remaining = (1 + 3) -3 = 1
`A^+`ions remaining = (3 + 1) -1 = 3
4 out of 8, ions are removed.
Percentage of number of ions remained `= 4/8 xx 100 =50`