Question

Which among the following is not a physical change?
A. Melting of solids to liquids
B. Vapourisation of liquids to gases
C. Liquefaction of gases to liquids
D. Decay of matter

Answer 1

Hint: We can say physical changes are changes in the state of matter without an accompanying change in composition and a new substance is formed that have different properties and composition from the original material in a chemical change.

Complete step by step answer:
We can define physical and chemical change as follows,
Physical change: An alteration of substance without changing its composition is called physical change. The change in state of a substance is the most common physical change. Example: Melting of an ice cube to form liquid water.
Chemical change: The conversion of one material to another is called chemical change (or) chemical reaction. Example: formation of water from hydrogen and oxygen is a chemical reaction because there is a difference in the composition of the material at the beginning and end of the process.
We can say melting of solids to liquids is physical change because one form of matter is converted into another form of matter. Here, solid is transformed to liquid. Hence, it is a physical change. Option (A) is incorrect.
Vapourisation of liquids to gases is also physical change because a liquid is transformed to gas that is one phase is changed to another phase. Hence, it is a physical change. Option (B) is incorrect.
Liquefaction of gases to liquids is also physical change because a gas is transformed to liquid i.e. one phase is changed to another phase. Hence, it is a physical change. Option (C) is incorrect.
Decomposition of matter is chemical change as it involves in the growth and activity of fungi, bacteria and other microorganisms

So, the correct answer is Option D”.

Note:
The visible physical and chemical change evidence happens when copper wire is heated in Bunsen flame, like platinum wire, copper wire also changes to a glowing red color when heated but on cooling a new substance black copper (II) has appeared.
Let us discuss some differences in physical and chemical change.

Physical change:
In physical change, the arrangement of molecules takes place while their actual composition remains the same.
Physical change is easily reversible.
In physical change, no formation of new substance is seen.
Physical change is a temporary change.
In physical change no energy is formed.
Physical change affects only physical properties like shape, size extra.
Example: boiling of water, melting of wax.

Chemical change:
In chemical change, there is complete change in molecular composition of a substance and a new substance is formed.
Chemical change is irreversible.
A chemical change is always accompanied by one or more new substances.
Chemical change is a permanent change.
In a chemical change energy is produced.
Chemical change changes both physical and chemical properties of the substance including composition.
Example: Digestion of food, rusting.