Question

Consider the following reaction: \[ \text{Ca}_3\text{P}_2 \xrightarrow{\text{HCl}} \text{X} + \text{Y} \uparrow \] Which of the following is not correct regarding Y?

• A. Yellow colored gas with rotten fish smell
• B. Lewis base
• C. In aqueous solution it decomposes in presence of light
• D. Explodes in contact with traces of $\text{Cl}_2$ vapors

Hint:

Phosphine ($\text{PH}_3$) is a colorless, highly poisonous gas with a rotten fish smell.
Pure $\text{PH}_3$ is non-inflammable, but it becomes inflammable in the presence of impurities like $\text{P}_2\text{H}_4$ or $\text{P}_4$ vapors.

Answer 1

The Correct Option is A

Step 1: Balance the reaction to find Y.
\[ \text{Ca}_3\text{P}_2 + 6\text{HCl} \rightarrow 3\text{CaCl}_2 + 2\text{PH}_3\uparrow \] So Y is phosphine gas, $\text{PH}_3$.
Step 2: Check the physical description first.
Phosphine is actually a colourless gas with a fishy or garlicky smell, not yellow, so this claim about colour is already off.
Step 3: Check the remaining chemical properties for consistency.
It does act as a Lewis base through the lone pair on phosphorus, it does decompose in light in aqueous solution, and it does explode on contact with traces of $\text{Cl}_2$ vapour, all three hold true.
Final answer: Option 1, the colour description is the one that's not correct.