How is the atomic mass of an atom determined and why are electrons not used in the calculation?

Achemistry student weighs out of phosphoric acid , a triprotic acid, into a volumetric flask and dilutes to the mark with distilled water. he plans to titrate the acid with solution. calculate the volume of solution the student will need to add to reach the final equivalence point. round your answer to significant digits.

The element that has the greatest electronegativity is

What is calcium oxide+diphosphorus pentoxide--> calcium phosphate balanced