Question

Which of the following is not correct?

• A. Potassium permanganate on heating gives potassium manganate and manganese dioxide only
• B. Phosphine is used in smoke screens
• C. Bleaching action of chlorine is due to oxidation
• D. Noble gases have very low boiling points

Hint:

Thermal decomposition of potassium permanganate releases oxygen gas in addition to potassium manganate and manganese dioxide.

Answer 1

The Correct Option is A

Step 1: Understand the thermal decomposition of KMnO$_4$.
When potassium permanganate (KMnO$_4$) is heated, it decomposes to give potassium manganate (K$_2$MnO$_4$), manganese dioxide (MnO$_2$), and oxygen (O$_2$), not just K$_2$MnO$_4$ and MnO$_2$: \[ 2 \, \text{KMnO}_4 \rightarrow \text{K}_2\text{MnO}_4 + \text{MnO}_2 + \text{O}_2 \uparrow \] Step 2: Verify other options.
- Phosphine is indeed used in smoke screens.
- Chlorine bleaches by oxidation.
- Noble gases have very low boiling points due to weak Van der Waals forces. Hence, option (1) is incorrect.