What is the layer located at an altitude of $50 \ km$ from the Earth's surface called?

The first trophic level in a food chain is always a green plant. Why?

Excessive exposure of humans to $UV$-rays results in:
$(i)$ Damage to immune system
$(ii)$ Damage to lungs
$(iii)$ Skin cancer
$(iv)$ Peptic ulcers

During heavy rain in a village,rainwater carried excessive fertilizers to a pond. How will it affect the fish population in the pond in the long run?

In the given food chain,suppose the amount of energy at the fourth trophic level is $5 \, kJ$,what will be the energy available at the producer level (in $, kJ$)?
Grass $\to$ Grasshopper $\to$ Frog $\to$ Snake $\to$ Hawk

Which of the following is an example of non-biodegradable waste?