`Na_(2)SO_(4)`, is an ionic compound. Therefore its formula unit mass is the same as its molecular mass
`2 xx 23+32+4xx16=142u`
(b) The mass of one mole of sulphur atoms =32u.
(c) 32 g of sulphur=1mol
12g of sulphur =`((12g))/((32g))xx1"mol"=0.375"mol"`
