How many effective `Cl^(-)` ions are present in the rock salt `NaCl` if ions along one axis joining opposite faces are removed? 

Answer

3

Explanation

If ions along one axis joining opposite face centres are removed `2Cl^(-)` at the faces are removed i.e. `2xx(1)/(2)=1`
`therefore` effective `Cl^(-)=4xx(1)/(2)=2` at, the remaining rface centres corners `=8xx(1)/(8)=1`
Total no. of `Cl^(-)=2+1=3`