Animated Solution for Chemistry - s and p-Block Elements: Match the reactions (in the given stoichiometry of the reactants) in List-I with one of their products given in List-II and choose the correct option.

Welcome to a fantastic exploration of p-block chemistry! Today, we are tackling a classic Matrix Match question from JEE Advanced that beautifully tests your grasp on the reactions of phosphorus and its compounds. This isn't just about memorizing equations; it's about understanding the underlying principles of oxidation states, disproportionation, and reducing power. Let's break down each reaction step-by-step.

The Hydrolysis of Phosphorus Trioxide

Our first reaction involves phosphorus trioxide (${\text{P}}_2{\text{O}}_3$) reacting with water.

When non-metal oxides undergo hydrolysis, they typically form oxyacids without changing their oxidation state. Let's calculate the oxidation state of phosphorus in ${\text{P}}_2{\text{O}}_3$. Oxygen is $-2$, so for three oxygen atoms, we have $-6$. This means the two phosphorus atoms must contribute $+6$, giving each phosphorus an oxidation state of $+3$.

When it reacts with water, it must form an acid where phosphorus remains in the $+3$ state. That acid is phosphorous acid, ${\text{H}}_3{\text{PO}}_3$.

So, for List-I entry (P), the correct match in List-II is (2).

The Disproportionation of White Phosphorus

Next up is a reaction that is an absolute favorite among examiners: white phosphorus (${\text{P}}_4$) reacting with an aqueous alkali like $\text{NaOH}$.

White phosphorus is highly reactive. When boiled with $\text{NaOH}$ in an inert atmosphere, it undergoes a disproportionation reaction. This means the elemental phosphorus (oxidation state $0$) is simultaneously oxidized and reduced.

It gets reduced to phosphine gas (${\text{PH}}_3$), where its oxidation state drops to $-3$. Simultaneously, it gets oxidized to form sodium hypophosphite (${\text{NaH}}_2{\text{PO}}_2$), where its oxidation state increases to $+1$.

Looking at our options in List-II, we see phosphine (${\text{PH}}_3$). Thus, entry (Q) matches with (3).

Chlorination with Phosphorus Pentachloride

In the third reaction, we have phosphorus pentachloride (${\text{PCl}}_5$) reacting with acetic acid (${\text{CH}}_3\text{COOH}$).

${\text{PCl}}_5$ is a notorious chlorinating agent. Its primary job in organic chemistry is to seek out hydroxyl ($-\text{OH}$) groups and replace them with chlorine atoms. When it attacks the $-\text{OH}$ group of acetic acid, it forms acetyl chloride (${\text{CH}}_3\text{COCl}$).

During this process, the ${\text{PCl}}_5$ molecule loses two chlorine atoms and picks up the oxygen, transforming into phosphorus oxychloride (${\text{POCl}}_3$). Hydrogen chloride ($\text{HCl}$) is also released as a byproduct.

From List-II, the matching product is clearly ${\text{POCl}}_3$. Therefore, entry (R) matches with (4).

The Reducing Power of Hypophosphorous Acid

Our final reaction features hypophosphorous acid (${\text{H}}_3{\text{PO}}_2$) reacting with silver nitrate (${\text{AgNO}}_3$).

To understand this reaction, we must look at the structure of ${\text{H}}_3{\text{PO}}_2$. It contains one $\text{P}=\text{O}$ bond, one $\text{P}-\text{OH}$ bond, and crucially, two direct $\text{P}-\text{H}$ bonds. These $\text{P}-\text{H}$ bonds are what give the acid its strong reducing character.

Because it is such a powerful reducing agent, it readily reduces the silver ions (${\text{Ag}}^{+}$) in silver nitrate down to metallic silver ($\text{Ag}$). In doing so, the hypophosphorous acid itself gets oxidized to its highest stable oxidation state, forming phosphoric acid (${\text{H}}_3{\text{PO}}_4$).

Looking at List-II, we find phosphoric acid (${\text{H}}_3{\text{PO}}_4$). So, entry (S) matches with (5).

By systematically analyzing the chemical principles behind each reaction, we've successfully decoded the entire matrix: - P matches with 2 - Q matches with 3 - R matches with 4 - S matches with 5

This problem is a beautiful reminder that inorganic chemistry isn't just a list of random facts. It's a logical system governed by oxidation states, molecular structure, and periodic trends. Keep looking for these patterns, and you'll master the p-block in no time!