The statement, "Four quantum numbers are required to describe completely an electron in an atom," is true.
Quantum numbers are used in physics to characterize all of the possible states of a quantum mechanical system. These numbers are "quantified" and given specific values.
Consider an electron in an atom.
The first quantum number used to describe the electron is called the principal or first quantum number. It is known as "n" and tells what shell the electron can be found in. "N" values start at 1 and continue to higher integers. The higher the "n" value, the farther out from the nucleus the electron is.
The next quantum number is called the azimuthal, orbital, or second quantum number and describes the shape of the electron's orbit. It is known as "l".
The third quantum number is called the magnetic quantum number and it tells the electron's orbit orientation compared to other orbits around the atom's nucleus. It is known as "m" or "ml".
The fourth quantum number is called the spin magnetic number and it describes the electron's spin direction properties. It is called "ms". It can take the value +1/2 or -1/2.