NCERT Class 10 Science Chapter 1 Chemical Reactions and Equations

Magnesium gets covered with a layer of magnesium oxide when kept in air for a long time. This layer hinders the burning of magnesium. Hence, it is to be cleaned before burning.

(i) Physical Change (ii) Chemical Change

A balanced chemical equation has an equal number of atoms of different elements in the reactants and products.
The chemical equations should be balanced to satisfy the law of conservation of mass.

i. Combination Reaction
ii. Decomposition Reaction
iii. Displacement Reaction
iv Double Displacement Reaction
v Redox Reaction

It is an undesirable change that occurs in metals when they are attacked by moisture, air, acids, and bases.
Example: Corrosion (rusting) of Iron: Fe2O3.nH2O (Hydrated iron oxide)

The taste and odor of food materials containing fat and oil change when they are left exposed to air for a long time. This is called Rancidity. It is caused due to the oxidation of fat and oil present in food materials.

By adding anti-oxidant.
Vacuum packing.
Replacing air by nitrogen.
Refrigeration of foodstuff.