A molecule `A_(2)B (Mw = 166.4)` occupies triclinic lattice with `a = 5 Å, b = 8 Å`, and `c = 4 Å`,. If the density of `AB_(2)` is `5.2 g cm^(-3)`, the number of molecules present in one unit cell is

Explanation

Volume of unit cell `=a xx b xx c`
`=5 xx 10^(-8) xx 8 xx 10^(-8) xx 4 xx 10^(-8)`
`rArr 1.6 xx 10^(-22) cm^(3)`
Mass of unit cell `=1.6 xx 10^(-22) xx 5.2 = 8.32 xx 10^(-22)`g
Number of molecules in one unit cell
`=(8.32 xx 10^(-22))/(166.4 g mol^(-1)) =3`