Orbitals which are equal in energy are referred to as

Degenerate Orbitals

~ Meaning ~

Electron orbitals that have the same energy levels are called degenerate orbitals. When assigning electrons to orbitals in determining electron configurations, the Aufbau principle states that lower energy orbitals are filled before higher energy orbitals.

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

            and  

since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.