How is biogas produced?

Which of the following statement$(s)$ is (are) incorrect reason for eutrophication?
$A$. excess usage of fertilisers
$B$. excess usage of detergents
$C$. dense plant population in water bodies
$D$. lack of nutrients in water bodies that prevent plant growth
Choose the most appropriate answer from the options given below:

How is excessive content of $CO_{2}$ responsible for global warming?

What is the reagent used for testing fluoride ion in water?

When plants and animals decay,the organic nitrogen is converted into inorganic nitrogen. The inorganic nitrogen is in the form of

Addition of phosphate fertilisers to water bodies causes