# NCERT Solutions for Class 9 Science

Find 100% accurate solutions for NCERT Class IX Science. All questions have been explained and solved step-by-step, to help you understand thoroughly. Free Download option available!

1.    °C = K – 273 = 293 – 273 = 20°C

°C = K – 273 = 470 – 273 = 197°C

2.    K = °C + 273 = 25 + 273 = 298 K

K = °C + 273 = 373 + 273 = 656 K

3.    a) Some substances possess the property of sublimation like camphor and naphthalene balls. Such substances directly change from solid to gaseous state without changing into liquid like ice → water → water vapour does. Therefore naphthalene balls disappear with time without leaving any solid.

b) Being a volatile substance (gets evaporated easily) perfumes change from liquid to gaseous state very fast. Those particles mix up with air particles and diffuse to reach our nostrils such that we get the smell of perfume sitting several metres away.

4.     Oxygen < water< sugar.

5.     At 25°C water is liquid, at 0°C water is solid(ice), at 100°C water is gas (water vapour).

6.    a) The room temperature is generally always more than 0°C and less than 100°C
and within this range water is a liquid so water at room temperature is a

b) The melting point of iron is much higher than the room temperature therefore an iron almirah is a solid at room temperature.

7.    While melting ice absorbs latent heat of melting from the surroundings and gets changed into water that makes the cooling effect more intense as compared to water at same temperature.

8.    As compared to boiling water it is observed that steam produces more severe burns since as the steam changes into boiling water it releases heat of condensation which is equivalent to latent heat of water result is more severe burning.

9.    A – Fusion (Heating – Melting)

B – Vapourisation

C – Cooling – Condensation (Liquefaction)

D – Cooling – Freezing (Solidification)

E – Sublimation

F – Solidification

10.  Chair, air, smell, almonds, cold drink and smell of perfume are matter.

11.  Since hot sizzling food has temperature higher than cold food and at higher
temperature diffusion rate (movement) of particles is very fast due to this the smell
of hot sizzling reaches us from several metres away.

12.  If diver has ability to cut through water in a swimming pool then it shows that the
particles of matter have a kind of force working between them. Because of this force
the particles of matter remain together till some external force is applied.

13.  The characteristics of particles of matter are as follows:

i) Particles of matter have gap between them.

ii) Particles of matter are in continuous motion

iii) Particles of matter have an attraction force between them to keep them
together.

14.  Arranging substances in their increasing order of densities:

Air< exhaust from chimneys< cotton< water< honey< chalk< iron.

15.  (a)

Solid

Particles are rigid and uncompressible.

They possess a definite shape and volume.

They don’t have the ability to flow.

Example: salt, sugar, chalk, gold, silver etc.

Liquid

Particles are not rigid but can be compressed to limited extent.

They have only a definite volume but acquire shape of container in which they are kept.

They can easily flow from higher to the lower level.

Example: water, alcohol, diesel, petrol etc.

Gas

Particles are not at all rigid and can be compressed easily.

They don’t have a definite shape or volume.

They can flow in all the possible directions.

Example: air, CNG, smoke etc.

(b)

Rigidity→ It is the property of matter to maintain its shape even if external

forces work and the solids show this property.

Compressibility → It is the property of matter to allow compression under high pressure and the gases show this property.

Fluidity → It is the property of a substance to easily .low and allow change in its shape under external forces and this property is exhibited by both liquids and gases.

Filling a gas container → Gases can be compressed easily hence they can be filled within a vessel at high pressure. This property of gases allows their convenient filling into a small container or cylinder and that also in a large volume. It also allows their easy transport from one place to the other eg CNG.

Shape→ According to the type of matter shape differs depending upon location of particles like Solids have definite shape while Liquids acquire the shape of their container and gases as such don’t have any shape.

Kinetic energy → It is the kind of energy present in an object when it is under motion as the particles of that object/matter are continuously moving therefore matter has kinetic energy. However greater is the movement more will be the kinetic energy and vice a versa i.e. solid < liquid < gas

Density → Mass per unit volume of a substance/matter is known as its density i.e. density = mass/volume.

16.  (a) Since the attraction force between particles of a gas is negligible i.e. extremely less hence particles freely move/flow in all possible directions as a result gas fills completely the vessel in which it is kept.

(b) Freely moving particles of gas hit the walls of its container continuously and randomly therefore such random and erratic motion of gas particles exerts pressure on the walls of the container.

(c) A wooden table particles are quite rigid, have a fixed location and also possess a definite shape and volume. Due to all these properties we should call a wooden table a solid substance.

(d) Air is a mixture of gases and since particles of gas are far apart so same is true for air therefore we can easily move our hand in air. But a solid block of wood is hard and rigid that resists any change in location of its particles hence we need a karate expert in case of a solid block of wood.

17.  Ice represents solid state of water. If we observe its 3D structure, a large empty space is found inside ice as a result it becomes less in weight as compared to water. Due to its specific structure though solid, ice floats on water.

18.  i) K= 273+°C

°C = K – 273=300 – 273 = 27°C

ii) °C = 573 – 273 = 300°C 2.

19.  100°C is the boiling point of water hence at both the temperatures water is in
gaseous state i.e. water vapour.

20.  During the change of state the heat or energy provided to particles of matter is utilized to take the particles of matter apart from each other as a result the temperature of substance or matter remains constant during change of state.

21.  If we decrease temperature and increasing pressure we can liquefy the atmospheric gases.

22.  On a hot dry day rate of evaporation is faster. In a desert cooler when exhaust fan is on, hot air enters through the straw mates and at this site evaporation of water takes place and that also at faster rate. It takes away heat from air so the air becomes cool even cooler on a hot dry day.

23.  During summers the water present on the surface of the earthen pot evaporates which causes the cooling effect. Besides earthen pot bears pores on it hence evaporation occurs continuously so is cooling.

24.  Some liquids get quickly vapourised and they are called volatile liquids. Acetone, petrol and perfume are also volatile liquids therefore they get heat from our palm and cause cooling.

25.  Saucer has a bigger surface area as compared to cup. Since evaporation is a surface phenomenon, by using a saucer instead of cup we are increasing the surface are for evaporation to occur. Faster evaporation of particles of tea or milk allows cooling and taking a sip becomes easier.

26.  Cotton is a good absorbant of water hence it absorbs sweat quite well and pores in the fabric expose that sweat to easy evaporation hence we should prefer wearing cotton clothes in summer.

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