#### A metai has a fcc lattice. The edge length of the unit cell is 404 pm. The density of the metal is 2.72 g cm-3. The molar mass of the metal is:(NA Avogadro's constant = 6.02 x 1023 mol-1) Option 1) 20 g mol-1 Option 2) 40 g mol-1 Option 3) 30 g mol-1 Option 4) 27 g mol-1

As we learnt in

Density of cubic unit cell -

- wherein

Where,

d = density of crystal

z = no. of effective constituent particles in one unit cell

M = molecular weight

a = edge length of unit cell

No = 6.022*1023

Density of cubic unit cell,

For an FCC,

Given that

Correct option is 4.

Option 1)

20 g mol-1

This option is incorrect.

Option 2)

40 g mol-1

This option is incorrect.

Option 3)

30 g mol-1

This option is incorrect.

Option 4)

27 g mol-1

This option is correct.