Questions

When atoms react they do so in order to reach the lowest energy, which is the most stable. The electrons orbitals will overlap in the way that reduces the energy the most. Orbitals of similar energy will produce the greatest stabilisation.The answer you gave isn't the whole story, it depends what species is reacting with what. The effective nuclear charge on the atom will affect the energy of the valance electrons.

Hence, the reactivity of an atom arises from the existence of unpaired electrons in the valence shell.

In India Coral Reefs can be found in Rameshwaram.

Coral reefs in India are one of the most ancient and dynamic ecosystems of India. The coral reefs not only provide a sanctuary to a myriad of marine life but also play a key role in protecting the coastline from erosion.

Coral reefs are diverse underwater ecosystems held together by calcium carbonate structures secreted by corals. Coral reefs are built by colonies of tiny animals found in marine water that contain few nutrients.