Answer:
(a) Naphthalene undergoes sublimation
easily i.e., the change of state of naphthalene from solid togas takes place
easily. Thus, naphthalene balls disappear with time without leaving any solid.
(1)
(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. (1)
(c) At room temperature
(25°C), water is a liquid because it has the following characteristic properties
of liquid
(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. (1)
(d) An iron almirah is a solid
at room temperature (25°C) because
(i) it has a definite shape and
volume like a solid at room temperature.
(ii) it is rigid as solid at
room temperature. (1)
(e) At 273 K, when ice melts, it
absorbs the energy equal to the latent heat of fusion from the surroundings,
therefore causes cooling effect. (1)
Or
(a) On releasing the pressure,
dry ice sublimes to vapour state without undergoing to liquid state. (1)
(b) (i) Melting point The
definite temperature at which a solid starts melting is called the melting
point of that solid, e.g., melting point of ice is 0°C or 273.16
K. (1)
(ii) Fusion The process
of conversion of a solid into liquid state on heating is called fusion or melting. (1)
(c) Diffusion is the process in
which molecules of a substance move from the place of (their) higher
concentration to the place of lower concentration. (1)
But during osmosis, the water
(or solvent) molecules move from (their) higher concentration to the
place of their lower concentration through a semipermeable membrane. Thus,
osmosis is termed as a special kind of diffusion. (1)
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