Calculate the number of moles in 2.2 g of K2SO4

What is the mass of sodium in 3 moles of sodium chloride

The content of manganese (mn) in steel was determined spectrophotometrically and with the use of the standard addition method. an unknown sample of mn from a digested steel sample gave an absorbance of 0.185 when analyzed spectrophotometrically. when 5.00 ml of solution containing 95.5 ppm mn was added to 50.0 ml of the unknown steel solution (digested sample), the absorbance was 0.248. calculate the concentration, in parts-per-million (ppm), of mn in the digested steel sample solution.

Structure of the atoms: discovery of the nucleus in 1909i need answering all of these questions