Give reasons for the following observatins:
(a) Air holes of a gas burner have to be adusted when the vessels being heated get blackened by the flame.
(b) Use of synthetic detergents causes pollution of water.

Give reasons for the following observations: (a) The element carbon forms a very large number of compounds. (b) Air holes of a gas burner have to be adjusted when the heated vessels get blackened by the flame. (c ) Use of synthetic detergents causes pollution of water.

Give reasons for the following. (a) Policemen regulating traffic often wear masks. (b) When water is heated , bubbles are observed.

Give reasons for the following. (a) Liquids can be taken in an open container while gas requires a closed container. (b) Honey cannot be poured into another container as easily as water (c) Gases flow more than liquids. (d) As water is subjected to heating, its temperature increases and becomes constant at 100^(@)C even though water is still there in the container and the supply of heat is continued. (e) When a solid substance is subjected to heating, it dissappears without leaving any liquid.

Give reason for the following : (a) Formation of NH_(3) from its elemets at constant pressure is accompained by a decrease in volume. (b) Nitric oxide turns in air. (c ) Copper dissolves in HNO_(3) but not in HCI. (d) Pb (NO_(3))_(2) on heating produces a pale yellow gas which on strong heating produces brown gas.

While determininig the melting point of ice it was observed that even when ice cubes were being moderates heated using the gas burner the temperature did not rise for sometime till the whole ice melted. Give the possible reason.