### NEET Solved Paper 2016 Question 20

##### Question: Lithium has a bcc structure. Its density is $ 530,kg,{m^{-3}} $ and its atomic mass is $ 6.94\text{ g mo}{l^{1~}} $ Calculate the edge length of a unit cell of Lithium metal. $ (N _{A}=6.02\times 10^{23}\text{ mo}{l^{1}}) $

#### Options:

A) 154 pm

B) 352 pm

C) 527 pm

D) 264 pm

## Show Answer

#### Answer:

Correct Answer: B

#### Solution:

$ \rho =\frac{Z\times M}{N _{A}\times a^{3}} $ For bcc structure $ Z=2,\rho =530\ kg\ {m^{-3}}=0.530\ g\ c{m^{-3}} $ $ 0.530=\frac{2\times 6.94}{6.02\times 10^{23}\times a^{3}} $ $ a^{3}=4.348\times {10^{-23}}\ cm^{3} $ $ a=3.52\times {10^{-8}}\ cm $ $ a=352\ pm $