Calculate the packing efficiency in Face Centred Cubic (FCC) structure.

Explanation

From `DeltaABC AC^(2)=AB^(2)+BC^(2)`
`b^(2)=a^(2)+a^(2)`
`b=sqrt2a`
`b=4r=sqrt2.a`
`a=(4r)/(sqrt2)`

`"Volume occpuied by 4 particles "=4xx((4)/(3))pir^(3)`
`"Volume of cube "=a^(3)=((4r)/(sqrt2))^(3)`
`therefore" Packing efficiency "=("Volume occupied by 4 particles")/("Volume of unit cell")xx100%`
`=(4xx((4)/(3))pir^(3))/(((4r)/(sqrt2))^(3))xx100%`
`=74%`