NCERT Solutions For Class 9 Science

Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume.

Give reasons for the following observation:
The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.

The mass per unit volume of a substance is called density. (density = mass/volume). Arrange the following in order of increasing density – air, exhaust from chimneys, honey, water, chalk, cotton and iron.

(a) Tabulate the differences in the characteristics of states of matter.
(b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.

Give reasons
(a) A gas fills completely the vessel in which it is kept.
(b) A gas exerts pressure on the walls of the container.
(c) A wooden table should be called a solid.
(d) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert.

Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.

Convert the following temperature to celsius scale:
a. 300 K   b. 573 K

What is the physical state of water at:
a. 250°C  b. 100°C ?

For any substance, why does the temperature remain constant during the change of state?

How does the water kept in an earthen pot (matka) become cool during summer?

Why does our palm feel cold when we put some acetone or petrol or perfume on it?

Convert the following temperatures to the celsius scale.
(a) 293 K   (b) 470 K

Convert the following temperatures to the kelvin scale.
(a) 25° C  (b) 373° C

Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.

Give two reasons to justify—
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.