Which notation designates a possible value for a principal energy level in an atom?

px

2

+1/2

s

2

Explanation:

There are four quantum numbers:

Principal quantum number (n)

Azimuthal quantum number (l)

Magnetic quantum number (ml)

Principal quantum number (n)

It tell about the energy levels. It is designated by n.

For example,

If n = 2

It means there are two energy level present.

Azimuthal quantum number (l)

The azimuthal quantum number describe the shape of orbitals. Its value for s, p, d, f ... are 0, 1, 2, 3. For l=3

(n-1)

4-1 = 3

it means principle quantum is 4 and electron is present in f subshell.

Magnetic quantum number (ml)

It describe the orientation of orbitals. Its values are - l to + l. For l=3 the ml will be - 3 - 2 - 1 0 + 1 + 2 + 3.

Spin quantum number (ms)

The spin quantum number tells the spin of electron either its clock wise (+1/2) or anti clock wise (-1/2).

If the electron is added in full empty orbital its spin will be + 1/2 because it occupy full empty. If electron is already present and another electron is added then its spin will be - 1/2.