Question

Which of the following is not a physical change
A.Boiling of water to give water vapour
B.Melting of ice to give water vapour
C.Dissolution of salt in water
D.Combustion of Liquefied Petroleum Gas

Answer 1

Hint: When a physical change happens there are no products formed. Only the state of the substance is getting changed.

Complete step by step answer:
 A Phase is defined as a homogeneous, physically distinct part of a system which is separated from the other part of the system by definite bounding surfaces.
Consider the system:
Ice \[ \leftrightarrow \] water \[ \leftrightarrow \] Vapour
It consists of three phases. One is solid phase, one liquid phase and one Gas phase.
Water is in Liquid phase. When we boil the water, it changes into Vapour state without any Chemical change. So, this Is a phase change. Because only state of the substance is getting changed.
Ice is in Solid phase. When Ice melts it changes into a liquid phase. This is also a physical change. There is no change in the chemical composition.
Salt is a solid. When it dissolves in water there are no new products formed. It is a physical change.
But Combustion of Liquefied Petroleum gas is not a physical change. It is a chemical change. Combustion LPG produces new substances. LPG burns to form water and Carbon monoxide. Incomplete combustion of LPG produces CO.
\[2{C_3}{H_8} + 9{O_2}\] \[ \rightarrow \] \[4C{O_2} + 2CO + 8{H_2}O\] + Heat

Hence, the answer is option (D) i.e Combustion of Petroleum gas

Note: Water system is a one component system. The changes of states include melting, sublimation, freezing, condensation. All state changes involve transfer of energy. During sublimation of a solid, it will directly convert into gas. During melting a solid gets converted into liquid. In the freezing process liquid is getting converted into solid. These are the main physical changes of water.