I believe the correct answer would be that it feels slippery. Being slippery or soapy is one characteristic of a base. This due to the fact that it dissolves the oils and fatty acids from the skin. Other characteristics would be that it turns litmus paper blue and has a bitter taste.
When landfills have a very poor maintenance, it would likely result in the release of harmful gases into the atmosphere. Among these poisonous gases released are carbon dioxide and methane in which if inhaled in an excessive amount, it could cause respiratory illnesses or it could be fatal.
3. Decreases
The concentration of hydrogen ions increasing creates an acid, which is 7 or below on the pH scale. If the pH value lessens from 7 to create an acid, that would mean it decreases.

The Correct choice is D. Fe + S = FeS
because, in nature Iron (Fe) and Sulphur (S) are found in mono - Atomic form. so, There will be 1 Fe atom reacting with 1 S atom to form FeS (Iron sulphide)
D, different niches like jobs so there are a lot of different species