D And F Block Elements – NEET UG ChemistryPractice Questions & PYQs

Sacrificial protection relies on covering a metal with a more electropositive coating that possesses a lower standard reduction potential than the underlying substrate. When iron is coated with zinc, the zinc preferentially oxidizes when exposed to corrosive environments because it acts as the more reactive anode in the electrochemical cell. Even if the outer coating gets scratched or damaged, the surrounding zinc continues to corrode in place of the iron beneath it, ensuring long-term durability.

Transition metals and their compounds possess unique catalytic abilities driven by variable oxidation states and surface adsorption, which direct specific chemical transformations. Vanadium pentoxide ($\mathrm{V}_2\mathrm{O}_5$) promotes the oxidation of sulfur dioxide to form sulfur trioxide during the industrial production of sulfuric acid, whereas iron serves as the fundamental catalyst for synthesizing ammonia from nitrogen and hydrogen. Palladium chloride ($\mathrm{PdCl}_2$) facilitates the conversion of ethyne into ethanal, and a nickel complex promotes the polymerization of alkynes.

When potassium permanganate undergoes thermal decomposition at 513 K, it breaks down into potassium manganate, manganese dioxide, and oxygen gas. The resulting potassium manganate contains manganese in the $+6$ oxidation state, corresponding to a single $d$-electron configuration. This lone unpaired electron imparts paramagnetism to the substance, while the manganate ion structure creates its distinctive emerald green appearance.

Pig iron absorbs significant quantities of carbon from the coke fuel during the blast furnace smelting process, establishing it as the primary and most abundant impurity. This raw metal typically contains around four percent carbon alongside trace amounts of silicon, manganese, and sulphur. Because of this high carbon concentration, pig iron remains brittle and hard before being refined into steel or cast iron.

Transition elements are defined as metals that have partially filled $d$ orbitals in their ground state or in any of their common oxidation states. Their outermost valence shell follows the general pattern where the outermost $s$ orbital is completely filled while the penultimate $(n-1) d$ subshell is progressively populated with one to ten electrons. This characteristic outer shell structure is compactly represented by the general electronic configuration $n s^{2}(n-1) d^{1-10}$.

The number of unpaired $d$-electrons depends on the valence shell electronic configuration of each ion filled according to Hund's rule. For iron two-plus, the neutral atom configuration $[Ar] 3d^6 4s^2$ loses two electrons from the $4s$ orbital to yield $[Ar] 3d^6$, leaving four unpaired electrons in the $3d$ subshell. In contrast, nitrogen three-plus possesses a core with no $d$-orbitals, while both zinc one-plus and copper one-plus have fully filled $3d^{10}$ configurations containing zero unpaired electrons. Thus, iron two-plus emerges with the maximum count among the given choices.

Metal carbonyl complexes feature transition metals coordinated to neutral ligands where the overall charge of the complex is zero and the ligands do not alter the formal charge. In $[\mathrm{Fe}(\mathrm{CO})_{5}]$, five carbon monoxide ligands act as neutral donor species surrounding the central iron atom. Setting up the algebraic sum for the oxidation state $x$ gives $x + 5(0) = 0$, which directly resolves to $x = 0$.

Surface hardening of steel through thermochemical treatments involves diffusing interstitial elements into the metal lattice to improve wear resistance and fatigue strength. During nitriding, the steel component is heated in an atmosphere of ammonia gas, which thermally dissociates to release reactive nitrogen atoms. These active nitrogen atoms diffuse into the surface layers to form hard iron nitrides that significantly enhance the mechanical durability of the material.

Transition metal complexes often display characteristic colours determined by their specific coordination environment and ligand-field transitions. While dissolving anhydrous copper sulfate, reacting copper sulfate with ammonium hydroxide, or mixing ferric chloride with sodium ferrocyanide all yield distinct blue solutions or precipitates, a different chemical outcome occurs with potassium ferrocyanide. The reaction between copper sulfate and potassium ferrocyanide produces cupric ferrocyanide, which forms a characteristic chocolate brown precipitate rather than any blue coloration.

Transition elements are defined by the progressive filling of the penultimate $d$-subshell, which corresponds to the $(n-1)$ energy level. As electrons are added to this inner shell, the outermost $n$ shell typically accommodates one or two electrons to maintain stability. This unique arrangement yields the characteristic general outer shell structure of $(n-1)d^{1-10}ns^{1-2}$ across the $d$-block series.

When calomel is treated with aqueous ammonium hydroxide, it undergoes a characteristic disproportionation process where mercury is simultaneously oxidized and reduced. This reaction yields a finely divided black precipitate of elemental mercury mixed with a white precipitate of mercury(II) amido chloride. The chemical transformation is expressed by the balanced equation $\mathrm{Hg}_2\mathrm{Cl}_2 + 2\mathrm{NH}_4\mathrm{OH} \rightarrow \mathrm{Hg} + \mathrm{HgNH}_2\mathrm{Cl} + \mathrm{NH}_4\mathrm{Cl} + 2\mathrm{H}_2\mathrm{O}$.

Stoichiometric equivalence in redox titrations is established using the mole ratio derived from the balanced chemical equation, which dictates that two moles of permanganate react with five moles of oxalate ions. Determining the millimoles of the permanganate solution by taking 20 mL of 0.1 M gives 2 mmol, which requires 5 mmol of oxalic acid for complete reaction based on the 2 to 5 stoichiometry. Evaluating the given choices confirms that 50 mL of 0.1 M oxalic acid provides exactly 5 mmol of the reactant, satisfying the equivalence condition.

As atomic numbers increase across the lanthanide series, a progressive and consistent reduction in atomic and ionic sizes occurs due to the poor shielding effect of inner $f$-orbitals. This phenomenon, widely recognized as lanthanide contraction, causes the ionic radii of trivalent lanthanides to steadily decrease rather than increase. Therefore, any assertion that these radii become larger with higher atomic numbers contradicts the fundamental electrostatic reality of increasing effective nuclear charge.

Metallic bonding strength depends heavily on the availability and willingness of valence electrons to participate in a shared electron sea, which is severely restricted in mercury due to its exceptionally high ionization energy. Because these outermost electrons are held tightly by the nucleus, they contribute very little to interatomic binding forces, resulting in unusually weak metallic interactions. This exceptionally diminished cohesion prevents the atoms from forming a rigid lattice at ordinary temperatures, allowing mercury to remain a liquid even at zero degrees Celsius.

Catalysis plays a fundamental role in industrial and synthetic chemistry, relying on specific transition metal systems to accelerate targeted chemical transformations. The industrial synthesis of ammonia through the Haber process employs an iron ($\mathrm{Fe}$) catalyst, whereas the Wacker oxidation converts alkenes to carbonyl compounds using palladium chloride ($\mathrm{PdCl}_2$). Additionally, homogeneous hydrogenation of alkenes is driven by the rhodium-based Wilkinson catalyst, denoted as $\mathrm{[(PPh_3)_3 RhCl]}$, and the coordination polymerization of olefins is facilitated by the Ziegler catalyst composed of titanium tetrachloride ($\mathrm{TiCl}_4$) combined with trimethylaluminum ($\mathrm{Al(CH_3)_3}$).

Ferromagnetic materials exhibit exceptionally strong cooperative alignment of atomic magnetic moments, making ferromagnetism fundamentally an extreme manifestation of paramagnetism. The electronic configuration of a chromium(II) ion with atomic number $24$ is $3d^4$, which yields four unpaired electrons. In contrast, a neodymium(III) ion with atomic number $60$ possesses a $4f^3$ configuration containing only three unpaired electrons, proving that the second statement is incorrect.

The reduction of manganese involves transitioning from a less stable $3d^4$ state in $\mathrm{Mn}^{3+}$ to a highly stable, half-filled $3d^5$ configuration in $\mathrm{Mn}^{2+}$ driven by a large gain in exchange energy. This pronounced thermodynamic stability makes the addition of an electron exceptionally favorable, pushing the reduction potential to a much more positive value compared to neighboring chromium or iron systems. Other transition metal couples do not benefit from gaining a symmetrically half-filled subshell upon reduction, keeping their standard potentials lower.

The spin-only magnetic moment of transition metal ions is determined by the formula $\mu = \sqrt{n(n+2)}$ BM, where $n$ represents the number of unpaired electrons. Both the chromium(II) and iron(II) ions contain four unpaired electrons in their respective $d$-orbitals, resulting in an identical magnetic moment of $\sqrt{24}$ BM. Similarly, both the titanium(III) and copper(II) ions possess exactly one unpaired electron, yielding a matching magnetic moment of $\sqrt{3}$ BM.

Unsaturation in organic compounds is typically identified using a mild oxidizing agent that selectively hydroxylates double and triple bonds. This specific reagent consists of a cold, dilute, aqueous solution of potassium permanganate. As it reacts with alkenes, the characteristic deep purple color disappears, producing a brown manganese dioxide precipitate and a corresponding vicinal diol.

Inner-transition metal spectra are characterized by well-defined electronic transitions that remain largely shielded from external ligand fields. Because the f-orbitals lie deep within the atom and experience minimal crystal field splitting, the resulting absorption bands appear as sharp, narrow lines rather than broad peaks. These specific spectral signatures arise directly from electronic excitations occurring strictly within the inner f-energy levels.