Question

Strontium oxide (SrO) crystal has cubic structure and has density $5$ g cm${}^{-3}$. If edge of the unit cell has length $520$ pm, the number of SrO formula units in each unit cell (atomic mass of $Sr=88$ amu) is :

Answer 1

We can use density formula as a tool to get the number of atoms.
Density $=\rho =\frac{ZM}{N_0{a}^3}$
By substituting necessary values, we get $5=\frac{X\times 88}{(6.022\times {10}^{23})\times (5.2\times {10}^{-8}{)}^3}$
On solving the above equation, we get the number of formula units as $4$.