CBSE 9th Chemistry | Matter-Nature and Behaviour (Long Answer Type Questions with Answers)

 Matter-Nature and Behaviour (Long Answer Type Questions with Answers)

Question 1.

(a) Justify the existence of matter in three states (i.e., solids, liquid, gaseous)

(b) Discuss the changes observed when ammonium chloride is heated.

(c) Convert -18°C to Kelvin scale.


Answer. (a)

The existence of matter in solid, liquid or gaseous state depends upon various factors such as interparticle space, interparticle forces of attraction etc. In solids we find the interparticle distance is minimum, which is slightly more in liquids and is maximum in gaseous state. The interparticles forces that bind constituent particles are maximum in case of solids, lesser in liquids and least in gases.

Answer. (b)

When ammonium chloride is heated it directly changes from solid state to gaseous state because it is a sublime substance.

Answer. (c)

–18°C = (– 18 + 273) K = 255K

Question 2. Answer the following:

(i) Why are naphthalene balls put in boxes used to keep woolen clothes?

(ii) How do aquatic animals survive under sea?

(iii) Comment: “Particle motion is blessing in disguise”.



Naphthalene balls are placed for preserving woolen clothes. In summers, when temperature is high, naphthalene balls sublime slowly (naphthalene is a sublime substance) to give vapours. These vapours act as germicides (i.e, germ killers) and kill the germs and bacteria which were likely to damage the woolen clothes.


The gases from the atmosphere diffuse and dissolve in water. These gases particularly oxygen (O2) and carbon dioxide (CO2) are essential for survival of aquatic animals.


In the absence of particle motion, the leakage of any poisonous gas would have remained stationary that may have caused harm in that place. Due to particle motion such a gas spreads over a large area and gets very much diluted and it causes lesser harm. In this way particle motion may be
considered as a blessing in disguise.


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