Nutrient enrichment of a lake will cause

Select the appropriate option for $FOAM$.

Soil erosion is prevented by ..........

Match the following concentrations of $DDT$ in an aquatic food chain:

Column-$I$	Column-$II$
$(a)$ Small fish	$(1) \;25 \;ppm$
$(b)$ Zooplankton	$(2) \;2 \;ppm$
$(c)$ Fish-eating birds	$(3) \;0.5 \;ppm$
$(d)$ Large fishes	$(4) \;0.04 \;ppm$

Identify the correct statements from the following:
$(i)$ $DDT$ is non-biodegradable.
$(ii)$ Heavy metals are responsible for biomagnification.
$(iii)$ High concentration of $DDT$ disturbs calcium metabolism in birds.
$(iv)$ The concentration of $DDT$ in large fish can be up to $2 \, ppm$.

Which of the following is incorrect?