# TEXTBOOK ANSWERS AND SOLUTIONS OF CBSE CLASS IX SCIENCE CHAPTER-1 Matter In Our Surroundings

1) Convert the following temperature to Celsius scale:
(a) 300 K
(b) 573 K
(a) 300 K = (300 273)°C = 27°C
(b) 573 K = (573 273)°C = 300°C
2) Convert the following
temperatures to Kelvin scale.
(a) 25°C
(b) 373°C
Kelvin is an SI unit of
temperature, where 0
°C =273.16 K (approximately
273 K)
(a) 25 °C = (25 + 273) K = 298 K
(b) 373 °C = (373 + 273) K = 646 K
3) 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.
(a) Naphthalene undergoes sublimation easily
i.e., the change of state of naphthalene from solid to gas takes
place easily. Thus, naphthalene balls disappear with time without leaving any
solid.
(b) Gaseous particles possess high speed and large spaces between
them. Particles of perfume diffuse into these gaseous particles at a very fast
rate and reach our nostrils. This enables us to smell the perfume from a
distance.
4) Arrange the following
substances in increasing order of forces of attraction between particles
−− water, sugar, oxygen.
< Sugar
5) What is the physical
state of water at
−−?
(a) 25°C
(b) 0°C
(c) 100°C
(a) Water at 25°C is present in the liquid
state.
(b) At 0 °C, water can exist as both
solid and liquid. At this temperature, after getting the heat equal to the
latent heat of fusion, the solid form of water i.e., ice starts changing into
its liquid form i.e., water.
(c) At 100 °C, water can exist as both
liquid and gas. At this temperature, after getting the heat equal to the latent
heat of vaporization, water starts changing from its liquid state to its gaseous
state, i.e., water vapour.
6) Give two reasons to justify
(a) Water at room
temperature is a liquid.
(b) an iron almirah is a
solid at room temperature.
a) (i) At room temperature,
water has no shape but has a fixed volume that is, it occupies the shape of the
container in which it is kept.
(ii) At room temperature,
water flows.
b)(i) it has
a definite shape and volume like a solid at room temperature.
(ii) it is rigid as solid
at room temperature.
7) Why is ice at 273 K
more effective in cooling than water at the same temperature?
Ice at 273 K has less energy
than water. Water possesses the additional latent heat of fusion. Hence, at 273
K, ice is more effective in cooling than water.
8) What
produces more severe burns, boiling water or steam?
energy than boiling water. It possesses the additional latent heat
of
vaporization. Therefore, burns produced by steam are more severe than those
produced by
boiling water.

9) Name A, B, C, D, E and
F in the following diagram showing change in its state. 