Which one of the following is not a mixture?
One of the following is not an exhaustible source of energy. This one is :
(a) natural gas.
(b) petroleum gas
(c) coal gas
(d) biogas
Which of the following is not a fossil fuel?(a) coal(b) petroleum gas(c) biogas(d) natural gas
Which of the following is a gas released by the usage of petroleum and coal but not poisonous?