Which of the following processes is a physical change rather than a chemical change?

Introduction / Context:
This question checks whether the learner can distinguish between physical and chemical changes. A physical change does not produce a new substance and is usually reversible by simple physical means. A chemical change leads to new substances with different properties, often accompanied by colour change, gas evolution, or energy release. Recognising these differences is a foundational skill in elementary chemistry.

Given Data / Assumptions:

• Four processes are listed: burning coal, burning wood, heating a platinum crucible, and heating potassium chlorate.
• We must identify the one that is purely physical.
• Chemical changes generally involve chemical reactions, while physical changes involve changes of state, shape, or size without altering composition.

Concept / Approach:
Burning processes, such as combustion of coal or wood, clearly involve chemical reactions with oxygen and produce new substances like carbon dioxide, water vapour, and ash. Heating of potassium chlorate decomposes the compound to potassium chloride and oxygen gas, which again is a chemical change. Heating a platinum crucible mainly causes expansion due to temperature rise and possibly glowing, but platinum is chemically very inert and does not react under ordinary heating, so no new substance is formed. This makes it a physical change.

Step-by-Step Solution:
Step 1: Examine burning of coal. Coal reacts with oxygen to form carbon dioxide, carbon monoxide, and ash, which are new substances, so this is a chemical change. Step 2: Examine burning of wood. Wood combustion produces carbon dioxide, water vapour, and ash, again a chemical change. Step 3: Examine heating of a platinum crucible. Platinum is a noble metal that resists oxidation. On heating, it may glow red or white but retains its chemical identity as metallic platinum, so this is a physical change. Step 4: Examine heating of potassium chlorate. Potassium chlorate decomposes on heating into potassium chloride and oxygen gas, clearly a chemical reaction.

Verification / Alternative Check:
The easiest way to verify is to ask whether a new chemical substance is produced. Both burning examples and the decomposition of potassium chlorate produce new substances. In contrast, heating a platinum crucible simply changes its temperature and colour, and the metal returns to its original state on cooling. Its mass and composition remain unchanged, confirming that this is a physical change.

Why Other Options Are Wrong:
Option A: Burning coal is combustion of carbon based fuel, which is a chemical process. Option B: Burning wood involves complex chemical reactions of cellulose, lignin, and other components with oxygen, again a chemical change. Option D: Heating potassium chlorate leads to thermal decomposition, forming new substances, which is a chemical reaction.

Common Pitfalls:
A common mistake is to assume that any process involving heat is a chemical change. Learners must remember that heat can cause both physical phenomena like expansion and state changes, and also chemical reactions, depending on the substance and conditions. Another pitfall is not knowing that platinum is highly inert, so they may mistakenly think it oxidises easily when heated, which is not the case in normal laboratory conditions.

Final Answer:
The process that represents a physical change is Heating of a platinum crucible.