List any two advantages associated with water stored in the ground.

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

We often observe domestic waste decomposing in the by lanes of our homes. List four ways to make the residents aware that the improper disposal of wastes is harmful to the environment and also for their own health.

What is meant by homologous series of carbon compounds? Classify the following carbon compounds into two homologous series and name them.

C₃H₄ C₃H₆ C₄H₆ C₄H₈ C₅H₈ C₅H₁₀

The elements ₄Be, ₁₂Mg and ₂₀Ca, each having two valence electrons in their valence shells, are in periods 2, 3 and 4 respectively of the modern periodic table. Answer the following questions associated with these elements, giving reason in each case:

(a) In which group should they be?

(b) Which one of them is least reactive?

(c) Which one of them has take largest atomic size?