Question

The number of atoms in 100 g of an FCC crystal
with density d = 10 g/cm3 and cell edge equal to
100 pm, is equal to
(1) 2 x 1025
(2) 1 x 1025
(3) 4 x 1025
(4) 3 x 1025
Х​

Answer 1

Explanation:

Correct option is A)

d=

a

3

×N

A

Z×M

where a is the edge of a unit cell

N

A

= Avogadro number (6.022×10

23

)

M = Molar mass

Z = number of atoms per unit cell

For FCC,

Z=4

From the given data, we can calculate the molar mass of the given substance as:

M=

Z

d×a

3

×N

A

Number of atoms =

molar mass(M)

Given mass

×N

A

Putting the value of M in the above equation we get-

Number of atoms =

d×a

3

×N

A

Given mass×Z×N

A

Number of atoms =

d×a

3

Given mass×Z

Putting the values we get:

Number of atoms=

10×(200×10

−10

)

3

100×4

=5×10

24

atoms

Hence, option A is correct