28) air can be considered a mixture. which statement describe air? a) air contains a fixed ratio of atoms. b) the components of air separate into visible layers. c) the components of air can be separated by chemical means. d) the exact mixture of components varies from point to point.

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.