You are given the balls and sticks models of six carbon atoms and fourteen hydrogen atoms and sufficient number of sticks. In how many ways one can join the models of six carbon atoms and fourteen hydrogen atoms to form different molecules of C₆H₁₄.

OR

Draw structural formulae of all the possible isomers of the compound with molecular formula C₃H₆O and also give their electron dot structures.

List two advantages associated with water harvesting at the community level.

Explain the following

(a) The reactivity of a piece of aluminium metal decreases if it is dipped in HNO₃

(b) Carbon cannot reduce the oxides of Na or Mg

(c) NaCl does not conduct electricity in solid state whereas it does conduct electricity in aqueous solution as well as in molten state

(d) Necessity of galvanisation of iron articles

(e) Metals like Na, K, Ca and Mg are never found in their free state in nature.

OR

Given below are the steps for extraction of copper from its ore.

(a) Write the equations of the reactions involved in roasting of copper (I) sulphide followed by its reduction.

(b) Draw a neat labelled diagram for electrolytic refining

Distinguish between pollination and fertilisation. Mention the site and product of fertilisation in a flower. Draw a neat, labelled diagram of a pistil showing pollen tube growth and its entry into the ovule.

OR

Reproduction is essentially a phenomenon that is not for survival of an individual but for continuation of a species. Justify

(a) Draw ray diagrams showing the image formation by a convex lens when an object is placed

(i) at twice the focal length of the lens

(ii) at infinity

(b) The image of a candle flame formed by a lens is obtained on a screen placed on the other side of the lens. If the image is three times the size of the flame and the distance between lens and image is 80 cm, at what distance has the candle been placed from the lens? What is the nature of the image and the lens?

OR

Write laws of refraction of light. Explain the same with the help of ray diagram, when a ray of light passes through a rectangular glass slab