Question

The process of obtaining salt by evaporation of sea water is known as :
A. chemical change
B. physical change
C. neutralisation
D. galvanisation

Answer 1

Hint: The process of obtaining salt from sea water involves the process of evaporation and is used on a large scale to obtain common salt from sea water. For solving this you must have a basic idea about different changes that occur in nature like what is a physical change , chemical change, neutralisation or galvanisation.

Complete step by step answer: For obtaining salt from sea water, sea water is trapped in shallow lakes and allowed to stand there. The heat of the sun gradually evaporates the water in the shallow lakes and common salt is left behind as a solid. Sea water has many salts dissolved in it. But to understand what type of a change is it first let’s study the given changes.
-Physical change - Physical changes only change the look of a substance but not its chemical composition.
-Chemical change - Chemical changes cause a substance to change into an entirely different substance with new chemical formula and composition. Chemical changes are also known as chemical reactions.
-Neutralisation - Neutralisation is a reaction of an acid with a base leading to the formation of a salt and water.
-Galvanisation - Galvanisation (or galvanizing as it is most commonly called) is the process of applying a protective zinc coating to iron or steel, to prevent them from rusting. The most common method is hot dip galvanizing, in which steel sections are submerged in a bath of molten zinc.
As we can see that the process of obtaining salt by the evaporation of seawater is a process of crystallization which is a reversible process and a physical change, these crystals will convert again in salt solution (seawater) by dissolving them in water. Thus it is a physical change.
Hence the correct option is B

Note: Do not get confused between a physical and a chemical change as some changes might appear physical but involve a chemical change and vice versa. And as obtaining salt from sea water is a reversible change means it is a physical change in nature and does not involve formation of any new substance or compound. Whereas the other three changes are irreversible and form a completely different compound on reaction.