UPSEE Solved Model Paper 7

Given
Number of molecules per unit cell, z = 4
Dimensions of unit cell a = 6.8

0

A

= 6.8 × 10−8 cm
b = 4.4

0

A

× 10−8 cm
c = 7.2

0

A

= 7.2 × 10−8 cm
Molar mass = 21.76
We have to calculate the density (ρ) of the crystal
Density of the crystal is given as:
ρ =

z×Molecular‌weight

V×Avogadro‌Number

... (i)
where, z = No of molecules per unit cell
V = Volume = a × b × c
Avogadro's number = 6.023 × 1023
On substituting all the values In equation (i). we get
ρ =
ρ =

4×21.76

215.×10−22×6.023×1023

ρ =

87.04

2.154×10−22×6.023×1023

ρ =

87.04

129.735

ρ = 0.6709gcm−3
Hence, option 'D' is correct.