What is the mass of one molecule of yellow phosphorus ? (Atomic mass , P = 30)

Options

A. `1.993 xx 10^(-22)` kg
B. `1.993 xx 10^(-19)` mg
C. `4.983 xx 10^(-20)` mg
D. `4.983 xx 10^(-23)` kg

Answer

B

Explanation

Yellow phosphorus is an impure form of white phosphorus `(P_(4))` .
Molecular mass of yellow phosphorus `(P_(4))`
`=4 xx 30 = 120`
`therefore` According to Avogadro's hypothesis ,
Mass of `6.022 xx 10^(23)` molecules = 120 g
and mass of 1 molecule = `(120 xx 1)/(6.022 xx 10^(23))`
`= 19.926 xx 10^(-23) g = 1.993 xx 10^(-22) g`
`= 1.993 xx 10^(-19) mg`