Which common non metal is a yellow solid at room temperature and produces a characteristic choking smell when burned in air?

Introduction / Context:
Many non metals have distinctive colours and odours, especially when they are heated or burned. Recognising these simple descriptive properties is useful in general chemistry and in everyday life. This question asks about a particular element that appears as a yellow solid at room temperature and gives off a strong, unpleasant smell when burned, which is associated with a common gas that can irritate the nose and throat.

Given Data / Assumptions:
- The element is yellow in its common solid form at room temperature.
- When burned in air, it produces a gas with a sharp, choking odour.
- The options list common halogens and non metals including sulphur and phosphorus.
- We assume ordinary classroom conditions and typical descriptions from basic chemistry.

Concept / Approach:
Elemental sulphur is a well known non metal that forms bright yellow crystals or powders. When sulphur is burned in air, it reacts with oxygen to form sulphur dioxide gas. Sulphur dioxide has a pungent, choking smell and can irritate the respiratory system. In contrast, chlorine and fluorine are greenish yellow and pale yellow gases respectively at room temperature, not yellow solids. Bromine is a reddish brown liquid at room temperature. Phosphorus can form white or red solids but is not typically described as a yellow solid that stinks when burned in the simple way outlined in the question. Therefore, the description points clearly to sulphur.

Step-by-Step Solution:
Step 1: Recall that elemental sulphur is usually encountered as a yellow crystalline solid used in matches and some industrial processes. Step 2: Remember that when sulphur is burned in oxygen, it forms sulphur dioxide, a gas with a strong and irritating smell. Step 3: Compare this with chlorine and fluorine, which are halogen gases at room temperature and not yellow solids. Step 4: Note that bromine is a dark reddish brown liquid, not a yellow solid, and its vapour has a different characteristic odour. Step 5: Recognise that phosphorus in its different forms does not match the simple description of a yellow solid that stinks when burned, making sulphur the best match.

Verification / Alternative check:
Laboratory demonstrations of burning sulphur show a blue flame and the immediate production of sulphur dioxide, which students are often warned not to inhale because of its sharp smell and potential to cause coughing. Textbooks describe sulphur as a yellow non metal and specifically mention sulphur dioxide as a poisonous gas with a pungent odour produced by burning sulphur. Everyday references to volcanic gases and industrial emissions also highlight sulphur compounds as sources of unpleasant smells. All these references are consistent with sulphur as the yellow element described in the question.

Why Other Options Are Wrong:
Chlorine and fluorine are gases under normal conditions and are not yellow solids that can be handled in the same way. Bromine is a dark liquid and, although it has a strong odour, it does not fit the description of a yellow element that stinks when burned. Phosphorus can produce various fumes when burned, but it is not typically identified by a yellow colour and the specific sulphur dioxide smell. Therefore, these alternatives do not match the described combination of colour and burning odour as well as sulphur does.

Common Pitfalls:
Students may focus only on odour and think of other smelly substances without considering the colour and physical state of the element. Another pitfall is confusing sulphur dioxide with other gases or assuming that any halogen gas with a strong smell might be the answer, even though the question clearly mentions a yellow solid. Keeping both the appearance and the burning smell in mind helps correctly identify sulphur as the element that fits this description.

Final Answer:
The yellow element that stinks when burned in air is Sulphur.