An element has the electron configuration [Ar] 3d^10 4s^2 4p^5. Which of the following statements about this element is correct?
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Correct answer
B. It is in Group 17 of the periodic table.
Principle or equation
The electron configuration determines the period and group. The highest principal quantum number indicates the period; the number of electrons in the outermost s and p orbitals indicates the group for main-group elements.
Why this answer is correct
The configuration [Ar] 3d^10 4s^2 4p^5 has the highest principal quantum number n=4, so it is in Period 4. The outermost electrons are 4s^2 4p^5, totaling 7 valence electrons, which places it in Group 17 (halogens). It is not a transition metal because the d subshell is completely filled (3d^10), and transition metals typically have partially filled d orbitals. Group 13 would have 3 valence electrons.
Example
The element is bromine (Br), which is in Group 17 and Period 4.
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