Which among the following are physical or chemical changes?

(a) Evaporation of petrol

(b) Burning of Liquefied Petroleum Gas (LPG)

(c) Heating of an iron rod to red hot.

(d) Curdling of milk

(e) Sublimation of solid ammonium chloride

(a) This is a Physical change.
Petrol just changes its state from the liquid form to the gaseous form because of the presence of energy in the form of heat. A change of state is a reversible reaction and hence, this is a Physical change.

(b) This is a Chemical change.
Burning of Liquefied Petroleum Gas releases energy and heat as its by products which cannot be converted back to the original reactant. The chemical composition of LPG has changed. Hence, it is a chemical reaction.

(c) This is a Physical change.
The temperature affects the metal temporarily. On reversing the temperature change, the metal goes back to its previous state. Hence, it is a physical state.

(d) This is a Chemical change.
The process of curdling of milk takes place due to bacteria. It is an irreversible reaction in which the composition of milk is changed and hence, a chemical change.

(e) This is a Physical change.
Energy in the form of heat has prompted solid ammonium chloride to evaporate. On reversing the temperature, it goes back to its previous solid state. Hence, this is a physical change.
A physical change in a substance doesn't change what the substance is. In a chemical change where there is a chemical reaction, a new substance is formed and energy is either given off or absorbed.