Question

Which of the following is a chemical change?
A. Melting of magnesium in air
B. Burning of magnesium in air
C. Dissolution of sugar in water
D. Blowing of wind

Answer 1

Hint: If the chemical composition is changing then it is a chemical change and if the chemical composition is remaining the same, then it is a physical change.

Complete answer:
A change in which the composition of a substance is altered is called a chemical change of matter. As a result, the original properties get changed and one or more new substances are formed.

In a chemical change loss or gain of energy takes place. No new atoms are created, and no atoms are destroyed. In a chemical reaction, reactants contact each other, bonds between atoms in the reactants are broken, and atoms rearrange and form new bonds to make the products.

The following can indicate that a chemical change has taken place: Change of odor. Change of color (for example, silver to reddish-brown when iron rusts). Change in temperature or energy, such as the production (exothermic) or loss (endothermic) of heat.

Burning of magnesium is chemical change in which magnesium oxide if formed

\[\text{2Mg+}{{\text{O}}_{2}}\to \text{2MgO}\]

Therefore, the correct choice is : (B) Burning of magnesium in air


Note:
Physical changes are those which are reversible and in such changes no new product(s) are formed. Chemical changes are those which are irreversible and involve formation of new product(s).