Which one of the following is not a gaseous biogeochemical cycle in ecosystem?

Which plant was introduced in India due to its beautiful mauve-colored flowers?

Identify the stage of hydrarch succession shown in the figure.

Which one of the following statements is incorrect for secondary succession?

Assertion : In tropical rain forests,$O-$ horizon and $A-$ horizon of soil profile are shallow and nutrient-poor.
Reason : Excessive growth of micro-organisms in the soil depletes its organic content.

Read the following statements carefully and answer the question:
$(1)$ Pyramids of number and biomass can be upright or inverted in an ecosystem.
$(2)$ Phosphorus and sulfur are sedimentary cycles.
$(3)$ The largest reservoir of carbon on Earth is found in the oceans.
$(4)$ The structural and functional unit of ecology is the ecosystem.
Which of the above statements are correct?