An element has the electron configuration 1s2 2s2 2p6 3s2 3p6 4s2 3d5. Which of the following statements about this element is correct?
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Correct answer
B. It is a transition metal.
Principle or equation
Elements with partially filled d subshells are transition metals. The period number is the highest principal quantum number of occupied orbitals; the group can be determined by the number of electrons in the outermost s and d orbitals.
Why this answer is correct
The configuration ends in 4s2 3d5, meaning the d subshell is partially filled, characteristic of a transition metal. It is in period 4 (highest n=4) and group 7 (2+5=7 valence electrons in s and d). It is not a noble gas, not period 3, and has 7 valence electrons if counting d electrons, or 2 if only s, but the correct classification is transition metal.
Example
Manganese (Mn) has this configuration and is a transition metal in period 4, group 7.
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