The correct answer of this question is : B) Nuclear energy.
EXPLANATION: B) Nuclear
As per the questions, there are four sources of energy known as coal, nuclear, gasoline and natural gas.
Out of these four sources, the nuclear source causes less air pollution. It is so because the byproducts produced in this nuclear fission process causes less air pollution as compared to the other sources like coal, natural gas etc.
Coal and other sources emit a lot of pollutants like carbon dioxide, nitrogen oxide and sulfur dioxide etc. which causes more air pollution.
Hence, the correct answer of the question is nuclear energy causes less air pollution.