Answer: Option (c) is the correct answer.
Explanation:
In open fire places, heat is releasing directly into the atmosphere. This heat is radiant in nature which does not harm the environment by being radiant.
Whereas it might be possible that not all of the available energy is extracted from the fuel. But sometimes all the energy from the fuel can be extracted.
But some fuels do produce toxic gases which harm the environment by polluting it and affecting the life of living beings.
Some fuels upon heating produce dust particles into the air and they also produce smoke. Therefore, both these factors affect the environment.
Thus, we can conclude that out of the given options radiant heat is released is not a problem with open fireplaces.
each, therefore the equivalent resistance of the circuit is