P Block Elements – NEET UG ChemistryPractice Questions & PYQs

Oxidation states are determined by assigning bonding electrons based on relative electronegativities, treating hydrogen as $+1$ and oxygen as $-2$. For hydrazine, ammonia, and hydroxylamine, the calculated oxidation states of nitrogen are $-2$, $-3$, and $-1$ respectively. In hydrazoic acid ($\mathrm{N}_{3}\mathrm{H}$), setting the algebraic sum of oxidation numbers to zero for $3x + 1(+1) = 0$ yields an average oxidation state of $-\frac{1}{3}$. Comparing these computed values shows that $-\frac{1}{3}$ is indeed the highest algebraic oxidation state among the options.

Nitrogen possesses a valence electronic configuration of $1s^2 2s^2 2p^3$, meaning its principal quantum number is two, which restricts its valence shell to only $s$ and $p$ subshells. Consequently, vacant $d$-orbitals are completely absent in its outer shell, strictly limiting its maximum covalency to four. This structural limitation makes the statement regarding the availability of $d$-orbitals entirely incorrect, whereas its high electronegativity, small molecular size, and non-metallic character are genuine properties.

White phosphorus exists as discrete, highly strained $\mathrm{P}_4$ tetrahedral molecules that interact strongly with non-polar solvents, making it readily soluble in carbon disulfide. In contrast, red phosphorus features a polymeric network structure composed of chained tetrahedral units, which renders it completely insoluble in carbon disulfide. Both allotropes share identical elemental atomic composition, undergo combustion upon heating in air, and can be thermally interconverted under specific conditions.

Bond energy depends on the balance between internuclear attraction and repulsive forces between non-bonding valence electrons of bonded atoms. Although oxygen is higher in group sixteen and typically forms shorter bonds, the small atomic size of oxygen brings its lone pairs of electrons extremely close together in an $\mathrm{O-O}$ single bond. This severe interelectronic repulsion destabilizes the bond and significantly lowers its dissociation energy, whereas the larger sulphur atom allows for an optimal covalent overlap without excessive lone pair crowding.

Dry slaked lime reacts with chlorine gas to form bleaching powder through a process where chlorine acts on calcium hydroxide. This manufacturing reaction yields calcium oxychloride, commonly known as bleaching powder, alongside water as a byproduct. The chemical transformation requires dry conditions at room temperature to ensure proper chlorine absorption and product stability.

Thermal dehydration of orthophosphoric acid proceeds in stepwise stages depending on the applied temperature, ultimately eliminating water molecules to form condensed phosphoric acids. At elevated thermal conditions reaching 875 K, complete loss of water converts the orthophosphoric acid into metaphosphoric acid according to $\mathrm{H}_3\mathrm{PO}_4 \rightarrow \mathrm{HPO}_3 + \mathrm{H}_2\mathrm{O}$. This transformation shifts the phosphorus-to-oxygen ratio by shedding structural hydroxyl groups to yield the corresponding cyclic or polymeric metaphosphate framework.

A chemical species is classified as paramagnetic when it possesses one or more unpaired electrons that generate a net magnetic moment within a magnetic field. Nitrogen dioxide contains an odd total of seventeen valence electrons, making complete electron pairing impossible throughout its molecular orbital framework and leaving a single unpaired electron on the central atom.

Phosphonium iodide is an ionic salt analogous to ammonium compounds that reacts vigorously with alkaline solutions. When combined with sodium hydroxide, a neutralization process occurs where the strong base abstracts a proton from the phosphonium cation. This breakdown results in the formation of sodium iodide, water, and volatile phosphine gas.

Covalent bonding achieves molecular stability through the mutual sharing of valence electrons to complete octets. A nitrogen atom has five valence electrons and requires three more to attain a stable octet structure. When two nitrogen atoms combine, they contribute three electrons each, creating a triple covalent bond composed of six shared bonding electrons.

Ammonia gas dissolves readily in water and reacts chemically with solvent molecules to form a weakly basic solution. This reversible hydration process transfers a proton from water to ammonia, producing both ammonium cations and hydroxide anions in dynamic equilibrium. Consequently, the resulting aqueous solution contains these characteristic ions alongside un-ionized dissolved ammonia molecules.

Intermolecular hydrogen bonding and van der Waals forces dictate the boiling points of group 15 hydrides. While boiling points generally increase down a group due to rising molecular mass and stronger dispersion forces, lighter hydrides like ammonia experience anomalous elevation because of extensive hydrogen bonding. Consequently, phosphine ($\mathrm{PH}_3$) lacks strong hydrogen bonding and has the smallest molecular mass among these hydrides, giving it the weakest intermolecular forces and thus the lowest boiling point.

Fractional distillation separates components of a liquid mixture by exploiting the differences in their boiling points. Once atmospheric air is liquefied, the distinct volatility of each component allows for clean separation inside a fractionating column. Because oxygen possesses a higher boiling point than nitrogen, nitrogen distills off first as a vapor while liquid oxygen remains behind in the column.

Commercial extraction of reactive elements depends on whether their ions can be safely discharged from an aqueous medium without preferential reduction or oxidation of water. Because chloride ions undergo oxidation at the anode more readily than water molecules under specific concentration conditions, concentrated sodium chloride brine undergoes electrolysis to produce chlorine gas industrially. In contrast, metals like sodium and aluminum have very negative reduction potentials and must be extracted through the electrolysis of molten anhydrous salts rather than aqueous solutions. Thus, chlorine stands out as the element commercially isolated via aqueous electrolysis.

Specific chemical absorbents are employed in gas analysis to selectively capture individual components from a mixture based on their unique chemical reactivity. Alkaline pyrogallol acts as an alkaline solution that rapidly and selectively absorbs molecular oxygen from gas streams. Meanwhile, oil of cinnamon contains specific organic constituents that selectively react with and capture ozone gas, allowing analytical chemists to quantify these species independently.

A lone pair consists of a pair of valence electrons that are not shared with another atom, completely filling a specific orbital in the outermost shell. Neutral chlorine possesses a valence configuration of $3s^2 3p^5$, whereas the chloride ion acquires an extra electron to achieve a noble gas configuration of $3s^2 3p^6$. This fully filled valence shell comprises one completely filled $s$ subshell and three completely filled $p$ subshells, resulting in exactly four unbonded electron pairs.

Bond polarity arises from the difference in electronegativity between the two bonded atoms, where a larger gap creates a more pronounced dipole moment. Comparing the Pauling electronegativity values of nitrogen (3.0), chlorine (3.0), oxygen (3.5), and fluorine (4.0) reveals that the $\text{N-Cl}$ and $\text{N-N}$ bonds have a difference of zero, the $\text{O-F}$ bond has a difference of 0.5, and the $\text{N-F}$ bond features the largest separation at 1.0. This maximum electronegativity gap makes the $\text{N-F}$ bond the most polar among the choices.

Electron affinity represents the energy released upon gaining an electron, which typically becomes more negative up and to the right of the periodic table. While halogens generally exhibit high electron affinities, fluorine deviates from this trend because its extremely small atomic radius creates high electron-electron repulsion within the compact valence shell. Chlorine avoids this intense spatial congestion and releases the maximum amount of energy when accepting an incoming electron.

The acidic character of non-metallic oxides intensifies as the electronegativity of the central element increases because a stronger pull on electron density facilitates proton release in water. Across the group containing nitrogen, phosphorus, arsenic, and antimony, electronegativity decreases markedly from top to bottom. Even though all these elements form pentoxides sharing a $+5$ oxidation state, nitrogen possesses the highest electronegativity by far, making its corresponding oxide exceptionally acidic.

Elements residing in the same vertical column of the periodic table share analogous valence shell properties, with succeeding periods accessed by incorporating specific shell capacities known as magic numbers. Summing the superscript electrons reveals a total atomic number of 15, which corresponds to phosphorus in the third period, while advancing directly downward to the fourth period within this group necessitates adding 18 to yield a final atomic number of 33.

Hypophosphorous acid is represented by the molecular formula $\mathrm{H}_{3}\mathrm{PO}_{2}$ and acts as a monobasic acid because it contains only a single replaceable hydrogen atom. Within its molecular framework, this lone acidic hydrogen is part of a hydroxyl group bonded to the central phosphorus atom, whereas the other two hydrogen atoms are directly attached to the phosphorus. This characteristic arrangement of atoms uniquely identifies the structure found in option C.