Question

Which transition element of the 3d series does not show variable oxidation state?

• A. Scandium (Sc)
• B. Titanium (Ti)
• C. Zinc (Zn)
• D. Chromium (Cr)

Hint:

Remember the common oxidation states of the first transition series: \[ \boxed{ \begin{aligned} Sc &\rightarrow +3\\ Ti &\rightarrow +2,\,+3,\,+4\\ V &\rightarrow +2\text{ to }+5\\ Cr &\rightarrow +2,\,+3,\,+6\\ Mn &\rightarrow +2\text{ to }+7 \end{aligned} } \] Scandium is the only transition element of the 3d series that predominantly shows only one oxidation state (\(+3\)).

Answer 1

The Correct Option is A

Concept: Transition elements generally exhibit variable oxidation states because both the \((n-1)d\) and \(ns\) electrons participate in bond formation. However, some elements predominantly exhibit only one stable oxidation state due to their electronic configuration. Scandium has the electronic configuration \[ \boxed{[Ar]\,3d^{1}4s^{2}.} \] It loses all three valence electrons to form \[ \boxed{Sc^{3+}} \] which has the stable noble gas configuration \[ \boxed{[Ar].} \] Hence, scandium predominantly exhibits only the \(+3\) oxidation state.

Step 1: Examine the oxidation states of the given elements.
\[ \begin{aligned} Sc &: +3\\ Ti &: +2,\;+3,\;+4\\ Cr &: +2,\;+3,\;+6\\ Zn &: +2 \end{aligned} \] Among the transition elements, scandium does not exhibit variable oxidation states.

Step 2: Reason for scandium's behaviour.
After losing three electrons, \[ Sc^{3+} \] attains the stable noble gas configuration \[ [Ar]. \] Further removal of electrons is highly difficult. Therefore, \[ \boxed{Sc\text{ exhibits only the }+3\text{ oxidation state}.} \]

Step 3: Choose the correct option.
Hence, \[ \boxed{\textbf{Option (A)}} \] is the correct answer.