What is stp? provide an answer using at least two different units of pressure and complete sentences?

The difference between the atomic number of an element and the element’s atomic mass is the number of ions.

Can someone me with 3 and 4 plz. this is for masteries test.

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.