Phosphorus has the molecular formula p4, and sulfur has the molecular formula s8. how many grams of phosphorus contain the same number of molecules as 7.88 g of sulfur?

1) Find the number of molecules in 7.88 g of sulfur

molar mass of S8 = 8*atomic mass of S = 8 * 32.0 g / mol = 256.0 g/mol

Number of moles  = mass in grams / atomic mass = 7.88 g / 256.0 g / mol = 0.0308 moles

2) Find the mass of 0.0308 moles of P4

mass = number of moles * molar mass

molar mass of P4 = 4 * atomic mass of P = 4 * 31 g/mol = 124 g/mol

mass of P4 = 0.0308 moles * 124 g/mol = 3.8192g ≈ 3.82 g.

3.82 grams of P4 will have the same number of molecules as 7.88 g of S8 (that is 0.0308 moles of molecules)