Test: Physical & Chemical Changes

Melting of ice is a physical change because no new substance is formed.

An atom is the smallest particle that forms molecules.

When two or more atom combine together in fixed ratio new compound is formed so, it is a chemical change.

Melting of ice is a reversible change while burning of matchstick, changing of milk into curd and germination of seed is chemical change.

Crystals of copper sulphate are prepared by the method of crystallization. It is an example of physical change.

So option D is correct answer. 

In chemical changes, molecules of substance rearrange to form a new substance with different property.

Boiling of water is a physical change:
Boiling of water produce water vapors. Chemically the water and water vapors composed of H₂O molecules. Here the change in physical state occurred. During this conversion The liquid is changed in to gas. On cooling these water vapors condensed into water. Hence it is a reversible reaction.

Sea water is a mixture because sea water contain a number of salts dissolved in it.

Galvanization or galvanizing is the process of applying a protective zinc coating to steel or iron, to prevent rusting. 

Rusting of iron is a chemical change because it happens due to a chemical reaction between iron and air in presence of moisture.

The electrons are transferred from Hydrogen to Oxygen , hence Oxygen is reduced and electrons are accepted by Oxygen from Hydrogen , hence Hydrogen is oxidised . Now , both oxidation and reduction are going together , therefore it is  a Redox (Reduction- Oxidation reaction) reaction 

Crystallisation is the  process of obtaining salt by the evaporation of sea water. 

When an apple is cut (or bruised), oxygen is introduced into the injured plant tissue. The oxygen  present in cells, polyphenol oxidase (PPO) enzymes in the chloroplasts rapidly oxidize phenolic compounds naturally present in the apple tissues to o-quinones, colorless precursors to brown-colored secondary products. So it's a chemical change.

Burning of magnesium ribbon in air is an example of chemical change. This is because when we burn magnesium ribbon in presence of oxygen it forms magnesium oxide . From magnesium oxide we cannot get back it's original state.

 One or more new substances are formed due to chemical change.