Question

The number of unit cells in 58.5g of NaCl are nearly(A)6 X 1020 (B)3 X 1022 (C)1.5 X 1023 (D)0.5 X 1024

Answer 1

Calculate the moles of NaCl as follows: 

molar mass of NaCl  = 58.5
mass = 58. g

moles = mass/molar mass
           = 58.5 / 58.5 
     1 mole

According to Avagadro's constant, 1 mole of any substance has exactly 6.022 × 10²³ molecules/atoms/unit cells.
 
Therefore in 58.5 g of NaCl there will be approximately 6.022 × 10²³ unit cells.

Answer 2

molar mass of NaCl  = 58.5

mass = 58. g

moles = mass/molar mass

          = 58.5 / 58.5 

    1 mole

According to Avagadro's constant, 1 mole of any substance has exactly 6.022 × 10²³ molecules/atoms/unit cells.

in bcc each unit cell contains 4 molecules of nacl

therefore, 6.022 x 10^23/4

= 1.5 x 10^23