Which natural resources are called the “biodiversity hot spots”? How these hot spots maintain ecological balance?

When a concave mirror is placed facing the Sun, the Sun’s rays converge to a point 10 cm from the mirror. Now, if you place a 2 cm long candles flame 20 cm away on the principal axis of the mirror, where would you place a screen to obtain the image of the candle? What would see the size of the image? Draw a ray diagram to justify your answer.

If you find coliform bacteria in a sample of water collected from a river, what would you conclude? Give a reason for such kind of water pollution.

What are isomers? “Isomers of the first three members of alkane series are not possible”. Give a reason to justify this statement and draw structures of two isomers of butane, C₄H₁₀.

An organic compound ‘X’ is a liquid at room temperature. It is also a very good solvent and has the molecular formula C₂H₆O. on oxidation ‘X’ gives ‘Y’ which give, break effervescence on reacting with NaHCO₃. X reacts with Y in the presence of conc.H₂SO₄ to give another compound ‘Z’ which has a pleasant smell. Identify X, Y and Z. also write chemical equations to show the formation of Y and Z.