what is the isotope notation for an element with a mass number of 49, and 21 protons? what is the atomic number and number of neutrons, as well?

49

Sc

21

In Isotope Notation, the mass number goes to the upper left of the chemical symbol and the number of protons (aka the atomic number) goes to the lower left of it. The number of neutrons is equal to the mass number minus the atomic number, which in this case is 28.