Which common non metal is a yellow solid at room temperature and produces a strong choking odour when it burns, due to formation of a pungent gas?

Introduction / Context:
Descriptive properties such as colour, physical state and smell are often used to identify elements and compounds in general chemistry. Sulphur and several halogens have distinctive appearances and odours, especially when heated or burned. This question asks specifically about a yellow solid that gives off a strong choking smell when burned because it forms a particular gas, making it important in environmental chemistry and pollution topics as well.

Given Data / Assumptions:
- The element is yellow and solid at room temperature under standard conditions.
- When it burns in air, it produces a gas with a strong, irritating smell.
- The options include bromine, sulphur, chlorine, fluorine and iodine, all non metals with different forms and properties.
- We assume common laboratory observations and textbook descriptions of these elements.

Concept / Approach:
Elemental sulphur exists as a bright yellow solid in the form of S8 rings. When sulphur burns in oxygen, it forms sulphur dioxide gas, which has a sharp, choking odour and can irritate the eyes and respiratory system. Bromine is a dark reddish brown liquid at room temperature, not a yellow solid. Chlorine and fluorine are gases under standard conditions, while iodine is a dark solid that sublimates to a purple vapour. None of these halogens match the combination of being a yellow solid and producing the specific choking smell associated with sulphur dioxide when burned.

Step-by-Step Solution:
Step 1: Identify that sulphur is commonly described as a yellow crystalline solid used in matches and some industrial processes. Step 2: Recall that burning sulphur in air produces sulphur dioxide, a gas with a distinctive choking smell. Step 3: Compare this with bromine, which is a dark red liquid at room temperature, not a yellow solid. Step 4: Note that chlorine and fluorine are gases at room temperature and are not described as yellow solids in standard conditions. Step 5: Recognise that iodine is a dark solid that gives a purple vapour, and does not fit the yellow solid description. The only option that fits both colour and odour when burned is sulphur.

Verification / Alternative check:
Classroom demonstrations often include burning sulphur on a deflagrating spoon and noting the blue flame and the production of sulphur dioxide fumes. Teachers frequently caution students about inhaling these fumes due to their choking effect. Textbooks describe sulphur as a yellow solid and list sulphur dioxide as a major gaseous pollutant with a sharp odour when sulphur is burned. Descriptions of halogens specify their typical colours and states, which do not match a yellow solid. These consistent references confirm that the element in question is sulphur.

Why Other Options Are Wrong:
Bromine is not a yellow solid but a dark brownish red liquid at room temperature and produces different vapours. Chlorine is a pale greenish gas, not a yellow solid, and is identified more by its bleaching action and sharp odour in gaseous form than by being burned. Fluorine is a pale yellow gas, extremely reactive, and not handled as a yellow solid in basic laboratory settings. Iodine is a dark solid that sublimes to a violet vapour and does not fit the yellow solid description. None of these halogens matches the combination of properties described in the question.

Common Pitfalls:
Students may remember that chlorine has a strong smell and incorrectly focus only on odour without considering physical state and colour. Another pitfall is confusing the colours of halogens with those of solid elements like sulphur. To avoid these errors, learners should match all aspects of the description, including colour, state and behaviour on burning. When all these factors are considered together, sulphur stands out clearly as the correct answer.

Final Answer:
The yellow solid element that stinks when burned, due to formation of sulphur dioxide gas, is Sulphur.