Which of the following statements is not correct?

Options

A. the number of Bravais lattices in which a crystal can ebh categorized in `44`.
B. The fraction of the total volume occupaied by the atoms in a primitive cell is `0.48`.
C. Molecular solids are generally volatile.
D. The number of `C` atoms in an unit cell of diamond is `4`.

Answer

2,4

Explanation

In a simple cubic lattice the edge length (or side of the cube) `a` and the radius of each particle `r` are related as
`a=2r`
The volume of the cubic unit cell =`a^(3)`
`=(2r)^(3)`
`=8r^(3)`
Since a simple cubic unit cell contains only `1` atom the volume of the occupied space `=4//3pir^(3)`
`:.` Packing efficiency
`=("volume of one atom")/("Volume of the cubic unit cell")xx100%` ltb rgt `=((4)/(3)pir^(3))/(8r^(3))xx100%`
`=(pi)/(6)xx100%`
`= 52.4%`
Here option `(2)` is not correct .
In diamond carbon atom have fcc arrangement with one `C`-atom on each body diagonal (i.e, occupying alternate tetrahedral voids). Structure of diamond is similar to that of zince blende `(ZnS)`
Net contribution of `C`-atoms on the corners.
`=8xx(1)/(8)=1`
Net contribution of `C`-atoms on face centres
`=6xx(1)/(2)=3`
Net contribution of `C`-atoms on `4` body diagonals
`=4xx1=4`
therefore total number `C`-atoms per unit cell of diamond is `1+3+4=8`. Hence option `(4)` is also not correct.