\(2KClO_3 \overset{653 - 873 K}{\longrightarrow}2KCl + 3O_2\)
On adding manganese dioxide to the above reaction, the subsequent decomposition takes place at
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Lower temperature
\( \ce{MnO2} \) acts as a catalyst in the decomposition of \( \ce{KClO3} \). A catalyst provides an alternative path with a lower activation energy, so the reaction proceeds at a useful rate at a lower temperature. Without \( \ce{MnO2} \), \( \ce{KClO3} \) must be heated to 653–873 K; with \( \ce{MnO2} \) the same decomposition takes place at a noticeably lower temperature. The catalyst itself is not used up.
Why the other options are incorrect
Option (2) Higher temperature — Incorrect. A higher temperature would mean the activation energy had been raised; a catalyst lowers it.
Option (3) The same temperature — Incorrect. If the temperature did not change, \( \ce{MnO2} \) would have no catalytic effect, but it increases the rate considerably.
Option (4) Unaltered by temperature change — Incorrect. The rate of decomposition still depends on temperature; the catalyst only lowers the temperature needed.
NCERT (2026-27 edition):
Effect of Catalyst – “A catalyst is a substance which increases the rate of a reaction without itself undergoing any permanent chemical change. For example, MnO2 catalyses the following reaction so as to increase its rate considerably.
2KClO3 → 2KCl + 3O2 (MnO2)”