Question

Assertion: The burning of a candle is both a physical and a chemical change.
Reason: Burning of candle melts the wax and hence the physical state of wax has changed from solid to liquid. Again the wax combines with atmospheric oxygen and changes to carbon dioxide, heat, and light.
A.Both assertion and reason are correct and reason is the correct explanation for assertion.
B.Both assertion and reason are correct but reason is not the correct explanation for assertion.
C.Assertion is correct but reason is incorrect
D.Both assertion and reason are incorrect.

Answer 1

A physical change only changes the appearance of the substance without any changes in its chemical composition. While a chemical change causes the entire chemical formula of the substance to change and form a new substance.

Complete step by step answer:
A candle is made up of paraffin wax or high molecular weight alkanes. These compounds burn in oxygen or react with oxygen to form water vapour and carbon dioxide according to the following reaction:
${C_{18}}{H_{38}} + 37{O_2} \to 18C + 18C{O_2} + 38{H_2}O$
Where, ${C_{18}}{H_{38}}$ is a typical component of the wax.
A change can be called a physical change only if the products formed from the reaction can be reverted back to the reactants, i.e., the reaction is reversible in nature. Here, in case of burning of the candle, two products, $C{O_2}$ and ${H_2}O$ do not react with each other to produce the reactants. Hence the reaction is not reversible in nature and the change is not a physical one but a chemical change.
So, the answer is that the assertion and the reason are incorrect.

Hence, option D is correct.

Note: Another way to solve this question is, any chemical change is marked by the breakage of old bonds and formation of new bonds. In the burning of candles also the $C - H$ bonds of the alkane and the $O = O$ are broken to form $C = O$ in carbon dioxide and $O - H$ bonds in water. This is only possible for a chemical change, not a physical change.