Step 1 - First, we need to transform kg into g. We need to multiply it by 1000:
158 kg = 158,000 g of phosphorus
Step 2 - Now we need to know the molar mass of phosphorus. Look for it at the periodic table. It is 30.97 g/mol.
Step 3 - We transform grams into moles:
30.97 g ---- 1 mol
158,000 g ---- x mol
x = 5,101.7 moles of phosphorus
Step 4 - We transform moles into atoms using Avogrado's constant:
6.022 x 10^23 ---- 1 mol
x ---- 5,101.7 moles of phosphorus
x = 3.072 x 10^27 atoms
If you want to calculate it in another way:
158000/30.97 x 6.022 x 10^23 = 3.072 x 10^27 atoms
Answer: There are 3.072 x 10^27 atoms of phosphorus