He principal quantum number, n, represents the: a sub level of an electron b main energy level of a proton c main energy level of an electron d sub level of a proton

Idon't understand what to put on the left lines i'm confused can anyone ?

1) this is the structure in the cell nucleus that houses a cell's genetic information

The characteristic of two different types of reactions are shown below. reaction a: electrons are gained by the atoms of an element. reaction b: protons are lost by the atom of and element. which statement is true about the atoms of the elements that participate in the two reactions? a: their identity changes in both reaction a and b. b: their identity changes in reaction a but not b. c: their identity changes in reaction b but not a. d: their identity remains the same.