The transition elements exhibit variable oxidation states because (n −1)d electrons can also participate in bonding as the energy difference between (n −1)d and ns orbitals is very small. The oxidation states of transition elements change in units of one whereas in p-block elements oxidation states normally differ by two units. The minimum oxidation state exhibited by a transition element is equal to the number of electrons in the ns orbital. The maximum oxidation state that can be exhibited by a transition element is equal to the total number of electrons present in both ns and (n −1)d orbitals. The elements in the middle exhibit more oxidation states, e.g., manganese exhibits from +2 to +7. The elements at the extreme ends exhibit a lesser number of oxidation states. This is because of the availability of lesser electrons to lose or to share in the earlier elements or too many d electrons due to which lesser number of unpaired electrons to share at the end. Due to anomalous electronic configuration, chromium and copper can exhibit a minimum oxidation state of +1. In the first series, the maximum oxidation state increases up to Mn and then decreases from Fe onwards. In the first series, Mn exhibits the maximum oxidation state +7. In the second series, a stable maximum oxidation state is exhibited by technetium, and an unstable maximum oxidation state +8 is exhibited by ruthenium. In the third series, stable maximum oxidation +8 is exhibited by osmium. The transition metal ions having completely filled and exactly half-filled d-sub level and those having octet in their outermost shell are stable. The stabilities of Cr³⁺ and Mn⁴⁺ ions is due to high lattice energy in solid state and high hydration energy in their aqueous solutions. Fe³⁺ ion is more stable than Fe²⁺ ion because of the stable half-filled 3d⁵ electronic configuration in Fe³⁺. In the last five elements of the 3d series, the 3d electrons are stabilized and require more energy for their removal because the 3d orbital contracts more and come nearer to the nucleus with an increase in nuclear charge. Thus in the last five elements, the +2 oxidation state becomes more stable (except Fe³⁺ ).

Identify the false statement among the following.

Chromium has the most stable oxidation state of +6

The correct answer is option 1. Chromium has the most stable oxidation state of +6.

Let us explain each statement in detail to identify the false one clearly:

1. Chromium has the most stable oxidation state of +6:

Chromium does exhibit a +6 oxidation state in compounds like \( \text{CrO}_4^{2-} \) (chromate) and \( \text{Cr}_2\text{O}_7^{2-} \) (dichromate). However, the +6 oxidation state is not the most stable for chromium. The +3 oxidation state (as in \( \text{Cr}^{3+} \)) is generally more stable due to the half-filled t2g orbital configuration which provides extra stability.

2. All the transition elements exhibit a common oxidation state +2:

This is not entirely true. While many transition elements do exhibit a +2 oxidation state due to the loss of two 4s electrons, not all transition elements show this oxidation state. For example, Scandium (Sc) primarily shows a +3 oxidation state and does not commonly exhibit a +2 state.

3. Ru and Os exhibit maximum oxidation state +8:

Ruthenium (Ru) and Osmium (Os) indeed exhibit a +8 oxidation state, which is the highest known oxidation state for elements.

4. The d-block element that does not exhibit variable oxidation state is zinc:

Zinc (Zn) commonly exhibits a +2 oxidation state and does not show variable oxidation states. This is because the Zn²⁺ ion has a completely filled d10 configuration, which is highly stable and not prone to further oxidation or reduction.

Given this analysis, the false statement is: Chromium has the most stable oxidation state of +6.

Chromium's +6 oxidation state is not the most stable; the +3 oxidation state is generally more stable.