Chemistry MCQs for NEET — Practice Questions with Answers

The elements which give the greatest number of oxidation states occur in or near the middle of the series. Manganese, for example, exhibits all the oxidation states from +2 to +7. (NCERT, Chapter: The d - and f - Block Elements, Page 97)

The lesser number of oxidation states at the extreme ends stems from either too few electrons to lose or share (Sc, Ti). Thus, early in the series scandium(II) is virtually unknown. (NCERT, Chapter: The d - and f - Block Elements, Page 97)

At the other end (of the series), the only oxidation state of zinc is +2 (no d electrons are involved). (NCERT, Chapter: The d - and f - Block Elements, Page 97)

The maximum oxidation states of reasonable stability correspond in value to the sum of the s and d electrons upto manganese ($Ti^{IV}O_2$, $V^{V}O_2^+$, $Cr^{VI}O_4^{2–}$, $Mn^{VII}O_4^{–}$). (NCERT, Chapter: The d - and f - Block Elements, Page 97)

The variability of oxidation states, a characteristic of transition elements, arises out of incomplete filling of d orbitals in such a way that their oxidation states differ from each other by unity, e.g., $V^{II}$, $V^{III}$, $V^{IV}$, $V^{V}$. (NCERT, Chapter: The d - and f - Block Elements, Page 97)

The variability of oxidation states... arises out of incomplete filling of d orbitals in such a way that their oxidation states differ from each other by unity, e.g., $V^{II}$, $V^{III}$, $V^{IV}$, $V^{V}$. This is in contrast with the variability of oxidation states of non transition elements where oxidation states normally differ by a unit of two. (NCERT, Chapter: The d - and f - Block Elements, Page 97)

Although in the p–block the lower oxidation states are favoured by the heavier members (due to inert pair effect), the opposite is true in the groups of d-block. For example, in group 6, Mo(VI) and W(VI) are found to be more stable than Cr(VI). (NCERT, Chapter: The d - and f - Block Elements, Page 97)

In group 6, Mo(VI) and W(VI) are found to be more stable than Cr(VI). Thus Cr(VI) in the form of dichromate in acidic medium is a strong oxidising agent, whereas $MoO_3$ and $WO_3$ are not. (NCERT, Chapter: The d - and f - Block Elements, Page 97)

Low oxidation states are found when a complex compound has ligands capable of $\pi$-acceptor character in addition to the $\sigma$-bonding. For example, in $Ni(CO)_4$ and $Fe(CO)_5$, the oxidation state of nickel and iron is zero. (NCERT, Chapter: The d - and f - Block Elements, Page 97 and 99)

When a particular oxidation state becomes less stable relative to other oxidation states, one lower, one higher, it is said to undergo disproportionation. (NCERT, Chapter: The d - and f - Block Elements, Page 105)