The element gallium has an atomic mass of 69.7 u and consists of two stable isotopes gallium-69 and gallium-71. the isotope gallium-69 has a mass of 68.9 u and a percent natural abundance of 60.4 %. the isotope gallium-71 has a percent natural abundance of 39.6 %. what is the mass of gallium-71

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.