Which is the hardest material ever known in the universe? 

Which phenomenon of light is behind the rainbow? 

Which of the following chemicals is used in fire extinguishers?

Nitrogen fixing bacteria lives in the root tumours of pea-plants is called:

Which of the following units is usually used to denote the intensity of pollution? 

'സാർസ്' രോഗം  ബാധിക്കുന്നത് മനുഷ്യശരീരത്തിലെ  ഏത്  അവയവത്തിനെ ആകുന്നു ?