15. Resources
1 Renewable and non-renewable resources
2 Potential and actual resources
3 Metallic and non-metallic resources
4 None of these
Explanation:
Renewable and non-renewable resources Resources can broadly be classified upon their availability — they are classified into renewable and non-renewable resources. Examples of non renewable resources are coal, crude oil etc. Examples of renewable resources are air, water, natural gas, wind, solar energy, etc. The resources which can be renewed or reproduced by physical, chemical or mechanical processes are known as renewable or replenishable resources. For example, solar and wind energy, water, forests and wildlife, etc. Non-renewable resources occur over a very long geological time. Minerals and fossil fuels are examples of such resources. These resources take millions of years in their formation. Some of the resources like metals are recyclable and some like fossil fuels cannot be recycled and get exhausted with their use.