Give reasons for the following: (a) Petroleum deposits are always associated with a layer of natural gas
The volatile products obtained by distillation of coal are passed through water.
( c) A mixture of acetylene and oxygen is used ofr welding metals.
( d) Anthratic coal is of better quality than bituminous coal.
( e) It is possible to perpare an alkane with one car-bon atom from a carboxylic acid with two carbon atoms.

Explanation

(a) The most volatile hydrocarbons under the earth s crust vaporise under high temperature and pressure conditions and form a layer of natural gas
(b) The volatile products obtained by distillation of coal may contain some water soluble gases such as `NH_3` as impurities. Therefore, they are passed through water to remove the volatile impurities
(c) Acetyleneu ndergoes combustion to produce large amount of heat. A mixture of acetylene and oxygen produce a tempereture of `3800^@C` which is higher than the meting points of metals . Therefore , it is used for welding purpose
(d) Anthracite coal contains 90 per cent and 10 per cent of other components such as sulphur or nitrogen. Bituminous coal contains 70 per cent of other components such as sulphur and nitrogen .As sulphur and nitrogen contribute much to the air water pollution anthracite is colsodered as a better type of coal
Decarboxylation involves removal of `CO_2` and resultant reducation of atoms from the parent corboxylic acid . Hence alkane with one carbon atom is prepared from carboxylic acid with two carbon atoms