Which of the following is the cleanest source of energy?

It is possible to produce algae based biofuels, but what is/are the likely limitation(s) of developing countries in promoting this industry? 

1. Production of algae based biofuels is possible in seas only and not on continents. 

2. Setting up and engineering the algae based biofuel production requires high level of expertise/technology until the construction is completed. 

3. Economically viable production necessitates the setting up of large scale facilities which may raise ecological and social concerns. 

Select the correct answer using the code given below:

With reference to two non-conventional energy sources called ‘coalbed methane’ and ‘shale gas’, consider the following ‘statements: 

(1) Coalbed methane is the pure methane gas extracted from coal seams, while shale gas is a mixture of propane and butane only that can be extracted from fine-grained sedimentary rocks. 

(2) In India abundant coalbed methane sources exist, but so far no shale gas sources have been found. 

Which of the statements given above is/are correct?

The relation between focal length 'f'‚ object distance 'u' and image distance 'v' in the case of reflection of light by a spherical mirror is given by_______.