Identify Non-Metal X Properties

The question asks to identify a non-metal 'X' based on three key properties:

• It occurs in nature in the free state.
• It reacts with hydrogen ($\text{H}_2$) to form a colorless, highly toxic gas.
• It oxidizes to form '$\text{XO}_2$', a colorless, pungent, and irritating gas.

Analyzing Element Properties

We need to evaluate the given options against these properties.

1. Free State Occurrence

Non-metals like Sulphur ($\text{S}$), Carbon ($\text{C}$), and Phosphorus ($\text{P}$) are known to occur in nature in their elemental (free) state. Nitrogen ($\text{N}$) exists as a diatomic molecule ($\text{N}_2$) in the atmosphere, which is also considered a free state.

2. Reaction with Hydrogen

The reaction of 'X' with $\text{H}_2$ produces a colorless, highly toxic gas.

• Sulphur reacts with $\text{H}_2$ to form Hydrogen Sulfide ($\text{H}_2\text{S}$). $\text{H}_2\text{S}$ is a colorless, highly toxic gas with a rotten egg smell.
• Phosphorus reacts with $\text{H}_2$ to form Phosphine ($\text{PH}_3$). $\text{PH}_3$ is a colorless, highly toxic gas.
• Carbon reacts with $\text{H}_2$ to form Methane ($\text{CH}_4$) and other hydrocarbons. $\text{CH}_4$ is colorless but not highly toxic.
• Nitrogen reacts with $\text{H}_2$ under specific conditions to form Ammonia ($\text{NH}_3$). $\text{NH}_3$ is colorless and pungent but not considered highly toxic in the same category as $\text{H}_2\text{S}$ or $\text{PH}_3$.

Based on this property, Sulphur and Phosphorus are strong candidates. Carbon and Nitrogen are less likely.

3. Oxidation to XO₂

The element 'X' is oxidized to '$\text{XO}_2$', which is described as a colorless, pungent, and irritating gas.

• Sulphur oxidizes to form Sulfur Dioxide ($\text{SO}_2$). $\text{SO}_2$ is a colorless, pungent, and irritating gas. This matches the description of '$\text{XO}_2$'.
• Phosphorus typically oxidizes to form oxides like Phosphorus Pentoxide ($\text{P}_4\text{O}_{10}$), which is a white solid, not a colorless gas of the type '$\text{XO}_2$'.
• Carbon oxidizes to Carbon Dioxide ($\text{CO}_2$) or Carbon Monoxide ($\text{CO}$). $\text{CO}_2$ is colorless and odorless. $\text{CO}$ is toxic but not usually described as pungent/irritating in this context, and it is not of the formula type '$\text{XO}_2$'.
• Nitrogen oxides include Nitrogen Dioxide ($\text{NO}_2$). $\text{NO}_2$ is reddish-brown, not colorless, although it is pungent and irritating.

Sulphur perfectly fits the description of forming the oxide '$\text{XO}_2$'.

Conclusion: Element X Identification

By evaluating all the properties:

• Sulphur occurs in the free state.
• Sulphur forms $\text{H}_2\text{S}$, a colorless, highly toxic gas.
• Sulphur oxidizes to $\text{SO}_2$, a colorless, pungent, and irritating gas.

Therefore, the non-metal 'X' is Sulphur.

Final Answer: The final answer is Sulphur