The average atomic mass of boron is 10.81 amu. Based on the atomic mass of B-10 and the relative abundances of the boron isotopes, what is the atomic
mass of B-11?
Isotope
Atomic mass (amu)
Relative abundance (%)
B-10
10.013
19.9
B-11
80.1
O A. 12.434 amu
OB. 11.009 amu
O C. 11.801 amu
O D. 9.084 amu

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.