How many unit cells are present in a cube - shaped ideal crystal of NaCl of mass 1.00 g ? [ atomic masses : Na =23,Cl-=35.5]

Options

A. ` 5.14 xx 10^(21)`
B. ` 1.28 xx 10^(21)`
C. `1.71xx 10^(21)`
D. `2.57 xx 10^(21)`

Answer

C

Explanation

One unit cell has 4 NaCl units, i.e, has mass
`(4 xx 58.5)/(6.-02 xx 10^(23)) g`
No. of unit cells is 1 g = `(6.02 xx 10^(23))/(4xx 58.5)`
` = 2 . 57 xx 10^(21)`