Combustion of hydrocarbons such as methane (CH) produces carbon dioxide, a "greenhouse gas." Greenhouse gases in the Earth's atmosphere can trap the
Sun's heat, raising the average temperature of the Earth. For this reason there has been a great deal of international discussion about whether to regulate the
production of carbon dioxide.

Carbondioxide is a greenhouse gas which is responsible for the global warming of the earth and also acidification of ocean water which makes the water unsuitable for marine organisms. This concentration of carbondioxide gas is reduced by planting more trees because plants reduce the amount of carbondioxide gas in the atmosphere by absorbing it in the process of photosynthesis. Less consumption of fossil fuels is also considered a good method to decrease carbondioxide concentration.

answer; i believe that the correct answer is (a) potassium(k)