The correct statement is (a) Sun can be taken as an inexhaustible source of energy.
Explanation: The Sun has been radiating energy for billions of years and is expected to continue doing so for many more billions, making it a practically inexhaustible source.
Why the other options are incorrect:
(b) There is infinite storage of fossil fuel inside the earth:
Fossil fuels are formed over millions of years from organic matter. While there are large reserves, they are not infinite and are considered a non-renewable resource.
(c) Hydro and wind energy plants are non polluting sources of energy:
While hydro and wind energy are considered renewable and relatively clean sources, they can still have some environmental impacts. For example, hydroelectric dams can alter river ecosystems and wind turbines can generate noise pollution.
(d) Waste from a nuclear power plant can be easily disposed off:
Nuclear waste is highly radioactive and requires safe and secure storage and disposal for long periods, making it a complex and challenging issue.