P Block Elements – JEE Main ChemistryPractice Questions & PYQs

The stability of the $+1$ oxidation state for Group 13 elements is primarily dictated by the inert pair effect, which describes the increasing reluctance of the valence $ns^2$ electron pair to participate in chemical bonding as the principal quantum number increases. Because inner $d$ and $f$ orbitals provide poor shielding for the nuclear charge, the valence $ns^2$ electrons are held more strongly toward the bottom of the group, effectively favoring the lower $+1$ oxidation state over the $+3$ state. This progressive stabilization of the $+1$ state results in the stability order of $\mathrm{Al} < \mathrm{Ga} < \mathrm{In} < \mathrm{Tl}$.

Understanding the structural connectivity of nitrogen oxides requires examining their specific Lewis structures to identify whether a direct nitrogen-nitrogen linkage exists. Among the compounds provided, $\mathrm{N}_2\mathrm{O}$ possesses a direct $\mathrm{N}-\mathrm{N}$ bond, while $\mathrm{N}_2\mathrm{O}_3$ and $\mathrm{N}_2\mathrm{O}_4$ also feature direct nitrogen-nitrogen bonds connecting their respective nitrogen centers. Conversely, $\mathrm{N}_2\mathrm{O}_5$ is characterized by an $\mathrm{N}-\mathrm{O}-\mathrm{N}$ linkage where the two nitrogen atoms are separated by an oxygen atom rather than being directly bonded. Therefore, three of the four oxides listed contain the specified $\mathrm{N}-\mathrm{N}$ bond.

Qualitative analysis of anions relies on adding dilute acid to liberate characteristic gases, each identified by its unique reaction with specific indicators. The carbonate anion, $\mathrm{CO}_3^{2-}$, evolves $\mathrm{CO}_2$ with brisk effervescence to turn lime water milky, while sulfide, $\mathrm{S}^{2-}$, releases $\mathrm{H}_2\mathrm{S}$ that turns lead acetate paper black. Sulfite ions, $\mathrm{SO}_3^{2-}$, liberate $\mathrm{SO}_2$ which turns acidified potassium dichromate green, whereas nitrite ions, $\mathrm{NO}_2^{-}$, produce brown $\mathrm{NO}_2$ gas that turns starch-iodide paper blue.

Polythionic acids, represented by the chemical formula $\mathrm{H}_{2} \mathrm{S}_{x} \mathrm{O}_{6}$, feature a straight chain structure of sulfur atoms where the oxidation states of the atoms differ based on their position. The terminal sulfur atoms bonded to oxygen groups maintain an oxidation state of +5, while the internal sulfur atoms positioned within the chain exist in the 0 oxidation state.

The disproportionation of elemental sulfur in an alkaline environment is a redox process where sulfur is simultaneously reduced to sulfide ions and oxidized to thiosulfate ions. This reaction is managed by balancing two separate half-equations: the reduction of sulfur to $\mathrm{S}^{2-}$ consuming 16 electrons and the oxidation of sulfur to $\mathrm{S}_{2}\mathrm{O}_{3}^{2-}$ requiring 12 water molecules and producing 24 protons along with 16 electrons. Combining these produces $2\,\mathrm{S}_{8} + 12\,\mathrm{H}_{2}\mathrm{O} \rightarrow 8\,\mathrm{S}^{2-} + 4\,\mathrm{S}_{2}\mathrm{O}_{3}^{2-} + 24\,\mathrm{H}^{+}$, and adding 24 hydroxide ions to both sides neutralizes the protons to form water. This yields $2\,\mathrm{S}_{8} + 12\,\mathrm{H}_{2}\mathrm{O} + 24\,\mathrm{OH}^{-} \rightarrow 8\,\mathrm{S}^{2-} + 4\,\mathrm{S}_{2}\mathrm{O}_{3}^{2-} + 24\,\mathrm{H}_{2}\mathrm{O}$, which simplifies upon removing excess water and dividing the stoichiometry by two to reach $\mathrm{S}_{8} + 12\,\mathrm{OH}^{-} \rightarrow 4\,\mathrm{S}^{2-} + 2\,\mathrm{S}_{2}\mathrm{O}_{3}^{2-} + 6\,\mathrm{H}_{2}\mathrm{O}$. Comparing this result to the provided expression reveals the value of the coefficient $a$ is 12.

When concentrated nitric acid is mixed with phosphorus pentoxide in a 4:1 molar ratio, the dehydrating action of the phosphorus pentoxide removes water from the nitric acid to produce dinitrogen pentoxide and metaphosphoric acid according to the equation $4 {HNO}_{3} + {P}_{4} {O}_{10} \rightarrow 2 {N}_{2} {O}_{5} + ({HPO}_{3})_{4}$. Because ${N}_{2} {O}_{5}$ is a non-metallic oxide in which nitrogen is in its highest oxidation state, it acts as an acid anhydride, demonstrating that it is characteristically acidic in nature.

The term chalcogens refers specifically to the elements belonging to the oxygen family found in the periodic table. This group is composed of the elements Oxygen, Sulfur, Selenium, Tellurium, and Polonium. Only the list containing Selenium, Tellurium, and Polonium accurately identifies members of this particular chemical family.

The electrolytic oxidation of a concentrated acidified sulphate solution serves as an industrial method to synthesize peroxydisulfuric acid. During this process, the anodic discharge of sulphate species leads to the formation of ${H}_{2} {S}_{2} {O}_{8}$, which incorporates a peroxide linkage between the two sulphur centers, represented by the structural formula ${HO}_{3} {SOOSO}_{3} {H}$.

Paramagnetism is observed in species that possess unpaired electrons, a principle governed by molecular orbital theory. The $S_{2}$ molecule is paramagnetic because, like $O_{2}$, it contains unpaired electrons within its molecular orbitals. In contrast, both $\alpha$-sulphur and $\beta$-sulphur exist as $S_{8}$ structures where every electron is paired, making these forms diamagnetic rather than paramagnetic.

The observation that a gas turns acidified potassium dichromate paper green signifies a redox reaction where the orange dichromate ion, containing chromium in the $+6$ oxidation state, is reduced to the green chromium(III) ion. Since sulfur trioxide ($\mathrm{SO}_3$) features sulfur in its maximum $+6$ oxidation state and cannot act as a reducing agent, the gas $X$ must be sulfur dioxide ($\mathrm{SO}_2$). When this sulfur dioxide reacts within the acidic medium of the dichromate, it undergoes oxidation while reducing the chromium, ultimately forming chromium(III) sulfate, represented as $\mathrm{Cr}_2(\mathrm{SO}_4)_3$, as the final green product $Y$.

The stability of coordination complexes involving group-14 elements is primarily governed by the steric constraints between the central atom and its surrounding ligands. Because the silicon atom is relatively small, it lacks the necessary space to accommodate six large chlorine atoms without experiencing severe steric crowding, which renders the structure unstable. Consequently, unlike complexes with smaller ligands such as $[{SiF}_{6}]^{2-}$, the ion $[{SiCl}_{6}]^{2-}$ is not known to exist.

A disproportionation reaction requires the central atom to exist in an intermediate oxidation state so it can simultaneously undergo oxidation and reduction. In the perbromate ion, $\mathrm{BrO}_4^{-}$, bromine is already at its maximum oxidation state of $+7$, meaning it lacks the capacity to lose further electrons and act as a reducing agent. Consequently, because bromine cannot be oxidized to a higher state, this species is unable to participate in a disproportionation reaction.

The xenon compound 'A' that yields $\mathrm{XeO}_{2}\mathrm{F}_{2}$ upon partial hydrolysis is xenon hexafluoride, $\mathrm{XeF}_{6}$, as represented by the balanced equation $\mathrm{XeF}_{6} + 2\mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{XeO}_{2}\mathrm{F}_{2} + 4\mathrm{HF}$. To calculate the total number of lone pairs in this molecule, first observe that the central xenon atom has eight valence electrons, and after forming six covalent bonds with fluorine, it retains one lone pair. Next, account for the fluorine atoms, where each of the six fluorine atoms possesses three lone pairs of electrons. Adding the lone pair on the xenon atom to the 18 total lone pairs provided by the six fluorine atoms results in a final sum of 19.

Industrial catalysts accelerate chemical reactions by providing alternative pathways with lower activation energies, ensuring higher efficiency in industrial processes. The Deacon's process for the production of chlorine uses ${CuCl}_{2}$ as a catalyst, while the Contact process for the synthesis of sulfuric acid typically relies on ${V}_{2} {O}_{5}$. In the petrochemical industry, the cracking of hydrocarbons is facilitated by shape-selective zeolites like ZSM-5, whereas the hydrogenation of vegetable oils into saturated fats is achieved using finely divided ${Ni}$ to lower the required reaction energy.

Determining whether a molecule contains a nitrogen-nitrogen bond requires examining its specific atomic connectivity. While oxides such as $\mathrm{N}_2\mathrm{O}$, $\mathrm{N}_2\mathrm{O}_3$, and $\mathrm{N}_2\mathrm{O}_4$ feature a direct connection between the two nitrogen atoms, $\mathrm{N}_2\mathrm{O}_5$ is distinct in its arrangement. In $\mathrm{N}_2\mathrm{O}_5$, the nitrogen atoms are separated by a bridging oxygen atom, creating an $\mathrm{N}-\mathrm{O}-\mathrm{N}$ linkage that ensures there is no direct nitrogen-nitrogen bond.

Halic (V) acids are defined as oxoacids in which the halogen atom exists in the +5 oxidation state. Chlorine, bromine, and iodine are the specific members of the halogen group that are capable of forming these stable compounds, which are represented by the chemical formulas $\mathrm{HClO}_3$, $\mathrm{HBrO}_3$, and $\mathrm{HIO}_3$. Based on these identified substances, there are 3 halogens that contribute to the formation of halic (V) acids.

The ability of a gas to be adsorbed onto a solid surface like activated charcoal is fundamentally determined by the ease with which it liquefies, a property indicated by its critical temperature. Because $SO_2$ possesses a higher critical temperature than $H_2$, it is more easily condensed and trapped by the adsorbent, leading to a significantly higher extent of adsorption. Consequently, the observed trend in adsorption is a direct consequence of these differences in critical temperatures, confirming that the stated reason logically accounts for the assertion.

When white phosphorus is boiled with a strong alkali in an inert atmosphere, it undergoes a disproportionation reaction where the phosphorus atoms are simultaneously oxidized and reduced. This process produces phosphine gas and sodium hypophosphite, which is identified as product A. The transformation is represented by the chemical equation $\mathrm{P}_4 + 3\mathrm{NaOH} + 3\mathrm{H}_2\mathrm{O} \rightarrow \mathrm{PH}_3 + 3\mathrm{NaH}_2\mathrm{PO}_2$.

The hypophosphite ion acts as a strong reducing agent due to the oxidation state of the phosphorus atom. When sodium hypophosphite reacts with an excess of aqueous silver nitrate, it reduces the silver ions to metallic silver, while the phosphorus is oxidized to phosphoric acid. This redox process follows the stoichiometry defined by the equation $\mathrm{NaH}_2\mathrm{PO}_2 + 4\mathrm{AgNO}_3 + 2\mathrm{H}_2\mathrm{O} \rightarrow 4\mathrm{Ag} + \mathrm{H}_3\mathrm{PO}_4 + \mathrm{NaNO}_3 + 3\mathrm{HNO}_3$. Based on the balanced coefficients, 1 mole of sodium hypophosphite reacts to produce 4 moles of silver.

The isomorphism between $TlI_3$ and $CsI_3$ arises because the $Tl^+$ and $Cs^+$ cations have nearly identical ionic radii, allowing them to form the same crystal lattice with the $I_3^-$ triiodide ion. In $TlI_3$, the thallium metal is present in the $+1$ oxidation state, a stability driven by the inert pair effect which keeps the $6s^2$ electron pair from participating in chemical bonding. This behavior is fundamentally linked to the electronic configuration of thallium, $[Xe] 4f^{14} 5d^{10} 6s^2 6p^1$, which contains a completely filled set of fourteen $f$-electrons. Because these $f$-electrons provide poor shielding, the effective nuclear charge on the $6s$ electrons increases, stabilizing the $+1$ state and ensuring that $Tl^+$ behaves similarly enough to $Cs^+$ to allow the two compounds to share an isomorphous structure.

The reducing strength of group 15 hydrides is determined by the bond energy between the central atom and hydrogen, which weakens significantly as the atomic size increases down the group. Because this decrease in bond stability makes the release of hydrogen progressively easier, $\text{BiH}_3$ possesses the highest reducing power of the series. Since bismuth is the only element in this group classified as a metal, it is the specific element identified by these properties.