An element has the electron configuration [Ar] 3d^3 4s^2. Which of the following statements about this element is correct?
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Correct answer
B. It is a transition metal with 3 valence electrons in the 4s and 3d subshells.
Principle or equation
The periodic table is organized by atomic number and electron configuration. Elements with partially filled d subshells are transition metals. The period number corresponds to the highest principal quantum number of occupied orbitals.
Why this answer is correct
The configuration [Ar] 3d^3 4s^2 indicates that the 3d subshell is partially filled (3 electrons), so the element is a transition metal. The highest occupied principal quantum number is 4, so it is in period 4. The valence electrons include the 4s and 3d electrons, totaling 5, but the option says 3 valence electrons in the 4s and 3d subshells, which is incorrect because there are 2 in 4s and 3 in 3d, total 5. However, the correct statement is that it is a transition metal. Option 1 is incorrect because it is not a main-group element. Option 3 is incorrect because noble gases have completely filled shells. Option 4 is incorrect because alkali metals have one s electron in the outermost shell.
Example
For vanadium, configuration [Ar] 3d^3 4s^2, it is a transition metal in period 4.
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