Question

A principal quantum number refers to:

a the numbered energy levels starting from the nucleus outward
b the total energy of an electron
c the maximum number of electrons at a given level
d the s, p, d, f levels

Answer 1

Answer: a) the numbered energy levels starting from the nucleus outward

Step-by-step explanation:

Principle Quantum Number: It describes the size of the orbital and the main energy level. It is represented by n. Where, n = 1,2,3,4....stands for K, L, M, N shell and so on..

Azimuthal Quantum Number : It describes the shape of the orbital. It is represented as 'l'. The value of l ranges from 0 to (n-1). For l = 0,1,2,3... the orbitals are s, p, d, f...

Magnetic Quantum Number : It describes the orientation of the orbitals. It is represented as
`m_l`. The value of this quantum number ranges from
`(-l\text{ to }+l)`. When l = 2, the value of
`m_l` will be -2, -1, 0, +1, +2.

Spin Quantum number : It describes the direction of electron spin. This is represented as
`m_s` The value of this is
`+(1)/(2)` for upward spin and
`-(1)/(2)` for downward spin.

Answer 2

A

Step-by-step explanation:

The principal quantum number describes the energy level of an electron (which start at the nucleus and go outward, as stated in the answer choice), so therefore, A is correct.

An example of this is n=1, which describes the first energy level. The elements on this level are Hydrogen and Helium. The principal quantum number also corresponds with the periods of the periodic table.