The peak intensity of radiation for a particular star occurs at a wavelength of 2.0 nanometers and what spectral band is this

Calculate the number of molecules present in 0.750 mol of mgo.

Ineed ! i have no clue how to do this problem.

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.