In which of the following interactions are both partners adversely affected?

Name the association in which one species produces a poisonous substance or a change in environmental conditions that is harmful to another species.

Select the mismatched pair regarding parasitism.

In which kind of population interaction, one species is harmed whereas the other is unaffected?

Match List-$I$ with List-$II$.

List-$I$	List-$II$
$A$. Both species are harmed	$I$. Predation
$B$. One species is harmed and the other is benefited	$II$. Mutualism
$C$. Both species are benefited	$III$. Competition
$D$. One is benefited while the other has no effect	$IV$. Commensalism

Choose the correct answer from the options given below:

For a limited resource, two closely related species compete for the same resource, which is known as $.........$, which keeps them in check in the environment.