When an element loses an electron it is generally taken away from the highest electron shell. The electron configuration of iron (Fe) is . The 4s orbital is farther away from the nucleus than the 3d orbital, therefore the electron configuration of Fe⁺ will be .

When determining electronic configuration, the answer is made much easier by starting with the next smallest noble gas in brackets. As a result, [Ar] is an appropriate way to incorporate every previous electron before argon.

After argon, vanadium has five other electrons to distribute, and because vanadium is a transitional element, it will fill its 3d subshells before filling the 4p subshells. The 4s subshell is filled first, and the last three electrons are placed into the 3d subshells.

[Ar]3d³4s²

A neutral atom of sodium would contain eleven electrons to balance out the charge of the eleven protons in the nucleus. We are asked, however, for the configuration of a sodium ion. Sodium is an alkali metal, meaning that it will ionize by losing only one electron, gaining a charge of . By losing one electron, sodium drops from having eleven electrons to ten. We will need to select the answer that shows an electron removed form the outermost shell.

Neutral sodium:

Sodium ion:

To determine where the outermost electrons are on a ground state element, we look at the periodic table, and see the row (or period) where that atom resides. This tells us how many electron shells that atom has, which is 2 for oxygen and 1 for hydrogen.

Finding the principle quantum number, which represents the size of the orbital, is easy. For a 2s or 2p orbital, it would be 2, for a 4s, 4p or 4d orbital it would be 4, etc. In this case, the correct answer is 3 (for 3p). Finding the azimuthal quantum number is slightly more difficult. Values of this number range from 0 to n-1. When n=3, it could theoretically equal 0, 1, or 2. But remember, this number describes the shape of the orbital, and is therefore just another way of stating the letter designation. When l = 0, the orbital is s, when l = 1, the orbital is p, and so on. Here, n = 3 and l = 1, signifying the 3p subshell.

The principle quantum number, , must be a positive integer.

The orbital angular quantum number, , ranges from  to , and is also an integer.

The magnetic quantum number, , ranges from  to , again is an integer.

The spin quantum number, , can have only a value of  or .

Of the choices given, the set  because the orbital angular quantum number must be less than the principle quantum number.

This question is testing your knowledge of quantum numbers. The principle quantum number () can be any positive integer value, although it is exceedingly rare that you will see anything greater than .

The azimuthal quantum number () has a range of values from zero to , and describes the subshell of the electron in question. In electron configuration, the azimuthal quantum number corresponds to the spdf orbitals.

The magnetic quantum number () has a range of values from to, and describes the specific orbital where the electron resides, within the subshell that was described by .

The magnetic spin number () has only two possible values: ^-  and ⁺. It describes the directionality of the electron's spin. In energy diagrams, these are represented by "up" and "down" arrows.

All except one of the given answer choices break rules.

Magnetic quantum number must be between positive and negative .

Azimuthal quantum number must be less than .

Azimuthal quantum number must be less than .

Quantum numbers are a type of coordinate system that describe the location and behavior of an electron in an atom. The principal quantum number or, , is the first quantum number. It signifies the energy shell of the electron. The principal quantum number is always greater than 0; therefore . An electron with  signifies that the electron is found within an orbital in the first shell (shell “K”). An electron with  is found in the second shell (shell “L”).  is found in the third shell (shell “M”), and so on and so forth. The principal quantum number can never be zero, so statement I is false.

Magnetic quantum number () is the third quantum number. It signifies the orientation of orbitals in space. The s orbital has one possible orientation in space, the p orbital has three possible orientations, and the d orbital has five possible orientations. The rule for magnetic quantum number is as follows:

 is the second quantum number. Therefore, if  (indicating the p orbital), then  can be either -1, 0, or 1 corresponding to the three possible orientations of the p orbital. Recall that each orbital can accommodate only two electrons. This means that both electrons in an orbital will have the same  quantum number. Statement II is false.

Angular momentum number, , is the second quantum number and it signifies the type of orbital. A 3d orbital signifies that it is a d orbital that is found in the third shell. The following is true for  values and the type of orbital.

 indicates an s orbital

 indicates a p orbital

 indicates a d orbital

 indicates an f orbital

Statement III suggests that a d orbital corresponds to the value , which is a true statements.

 is the second quantum number, and it signifies the type of orbital housing the electron (for example, s, p, d, or f).  is the third quantum number and it signifies the orientation of the orbital in space. The range of values for  depends on the given  value. The relationship is as follows:

Therefore, if , then  can have three different values: .

If , then  can have five different values: .

If , then the electron is found in a p orbital. A p orbital can have three different orientations in space; it can found along the x-axis, y-axis, or z-axis (corresponding to the three  values). An electron with  can be found in any one of these three p orbitals. Note that a shell always has three p orbitals and all of them are oriented in different regions in space. For example, if , then there are three 3p orbitals that are oriented along x, y, and z-axes, respectively.

An s orbital has a spherical shape. Shell “K” is the first shell of an atom (the first energy level). We cannot determine the shell of an electron without knowing the principle quantum number; therefore, we cannot conclude that the electron stated in this question is found in the first shell.