What are acids?

Ans: The substances that taste sour and turn blue litmus paper red are called acids.

What are bases?

Ans: The substances which are bitter in taste, feel soapy and turn red litmus paper blue are called bases.

What are neutral solutions?

Ans: The solutions which do not change the colour of either red or blue litmus paper are known as neutral solutions.

What are indicators?

Ans: The substances used to test whether a substance is acidic or basic are known as indicators.

What is breathing?

Ans: Breathing is a process in which air rich in oxygen is taken in and air rich in carbon dioxide is given out.

What is respiration?

Ans: The process of breakdown of food inside the cell with the release of energy is called respiration.

What is the difference between breathing and respiration?

Ans: Breathing is just a mechanical process of inhaling and exhaling air, while respiration is a complex process which involves breakdown (oxidation) of food in the cell with simultaneous release of energy. Carbon dioxide and water are also produced in this process.

What is inhalation?

Ans: The intake of air rich in oxygen is called inhalation.

What is light?

Ans: Light is a form of energy that is always in motion. It is light that enables us to see an object.

What are luminous objects?

Ans: Objects that have their own light, i.e., objects that emit light, are called luminous objects, e.g., Sun, stars, etc.

What is a beam of light?

Ans: A number of rays of light travelling together are called a beam of light.

What is a ray of light?

Ans: A straight line drawn from the source of light, which represents the straight path of light, is called a ray of light.

What is reflection of light?

Ans: The phenomenon of bouncing or bending of light by a surface back to the same medium, when light falls on it, is called reflection of light.

What are the seven constituent colours of sunlight?

Ans: These are red, orange, yellow, green, blue, indigo and violet.

What is a prism?

Ans: A prism is a piece of any transparent material (e.g., glass) which is bounded by two triangular and three rectangular surfaces.