Question

The sum of oxygen atoms in the formulae of peroxysulphuric acid and pyrosulphuric acid is

• A. 7
• B. 15
• C. 12
• D. 13

Hint:

Knowing the common oxyacids of sulfur and their formulae is crucial for solving such questions. Peroxysulphuric acid contains a peroxide linkage (-O-O-), leading to one extra oxygen compared to sulphuric acid. Pyrosulphuric acid is formed by the condensation of two sulphuric acid molecules with the loss of water.

Answer 1

The Correct Option is B

Step 1: Write the molecular formulae of the acids.
Peroxysulphuric acid (also known as Caro's acid) has the molecular formula: \[ \mathrm{H_2S_2O_8} \] It contains 8 oxygen atoms. Pyrosulphuric acid (also known as oleum) has the molecular formula: \[ \mathrm{H_2S_2O_7} \] It contains 7 oxygen atoms. 
Step 2: Add the total number of oxygen atoms.
\[ 8 \text{ (from } \mathrm{H_2S_2O_8}) + 7 \text{ (from } \mathrm{H_2S_2O_7}) = 15 \]