Question

124 amu of P4 will contain:(at mass of P=31) how many atoms or molecules of phosphorus?

Answer 1

124 amu is the molecular mass. (31*4)
124 g is the given mass. 
USING THE FORMULA,
The no.of molecules will be 6.022* 10 raised to the power 23

Answer 2

Answer:-

Atomic weight of $P_4$= 31 amu

Weight of $P_4=4\times 31=124 amu$

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$

Given mass of $P_4$ = 124 amu

Molar mass of  $P_4$ = 124 amu

$\text{Number of moles}=\frac{124}{124}=1mole$

1 mole of $P_4$ contains=$6.023\times 10^{23}$ molecules of $P_4$

1 mole of $P_4$ contains=$4\times 6.023\times 10^{23}=24.1\times 10^{23}$ atoms of $P_4$