Chemistry - CHEMICAL BONDING Question with Solution | TestHub

Solution:

The question asks to match the molecular formulas of oxy-acids with their common names.

(P) ${\mathrm{H}}_4{\mathrm{P}}_2{\mathrm{O}}_7$ is Pyrophosphoric acid, formed by the dehydration of two molecules of orthophosphoric acid:

$$2{\mathrm{H}}_3{\mathrm{PO}}_4\stackrel{-{\mathrm{H}}_2\mathrm{O}}{\to }{\mathrm{H}}_4{\mathrm{P}}_2{\mathrm{O}}_7$$

So, P $\to$ 4.

(Q) ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_8$ is Peroxodisulfuric acid, commonly known as Marshall's acid. It contains a peroxy (-O-O-) linkage.

So, Q $\to$ 5.

(R) ${\mathrm{H}}_2{\mathrm{SO}}_5$ is Peroxomonosulfuric acid, commonly known as Caro's acid. It also contains a peroxy (-O-O-) linkage.

So, R $\to$ 3.

(S) ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_7$ is Pyrosulphuric acid, also known as Oleum. It is formed by the dehydration of two molecules of sulfuric acid:

$$2{\mathrm{H}}_2{\mathrm{SO}}_4\stackrel{-{\mathrm{H}}_2\mathrm{O}}{\to }{\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_7$$

So, S $\to$ 1.

Matching these, we get: P $\to$ 4, Q $\to$ 5, R $\to$ 3, S $\to$ 1.

The final answer is $\boxed{B}$