States of Matter

5.35. When density of liquid and vapours becomes the same; the clear boundary between liquid and vapours disappears. This temperature is called critical temperature.

5.34. The temperature at which the vapour pressure of a liquid is equal to external pressure is called boiling point of liquid.

5.33. Molecules of liquids are held together byattractive intermolecular forces. Liquids havedefinite volume because molecules do notseparate from each other. However, moleculesof liquids can move past one another freely, therefore, liquids can flow, can be poured andcan assume the shape of the container in whichthese are stored.

5.32.  (c) F₂

5.31.  (b) frictional resistance

5.30.  (a) decreases

5.29.  (b) increases by three times

5.28. (b) directly proportional to its absolute temperature

5.27.  (c) At high altitudes atmospheric pressure is low. Therefore, liquids at high altitudes boil at lower temperatures in comparison to that at sea level. Since water boils at low temperature on hills, the pressure cooker is used for cooking food. In hospitals surgical instruments are sterilized in autoclaves in which boiling point of water is increased by increasing the pressure above the atmospheric pressure by using a weight covering the vent.

5.26.  (d) Compression brings the molecules in close vicinity and cooling slows down the movement of molecules therefore, intermolecular interactions may hold the closely and slowly moving molecules together and the gas liquifies.