Q13 of 58 Page 1

What is placenta? Explain its function in human female.

Placenta is a disc like tissue which is embedded in the uterine wall and contains villi on the embryo’s side of the tissue and mother’s side are blood spaces surrounding the villi.

It plays an important role as the embryo gets nourishment inside the mother’s body by a disc-like tissue placenta which gets developed between the uterus well and the embryo during the implantation. The nutrients, Oxygen and waste products are exchanged through this tissue.


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What is meant by power of a lens? Define its SI unit.

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The atomic number of an element 'X' is 20. Write

(a) its valency,


(b) whether it is a metal or non-metal,


(c) the formula of compound formed when the element 'X' reacts with an element 'Y' of atomic number 8.


Justify your answer in each case.

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How are fossils formed? State two methods of determining the age of fossils.

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A student focused the image of a candle flame on a white screen using a convex lens. He noted down the positions of the candle flame, screen and the lens as given below: Position of the candle flame = 12.0cm

Position of the lens= 50.0 cm


Position of the screen= 88.0 cm


(i)Find the focal length of the convex lens.


(ii)Find the position of the image of the candle flame if it is shifted towards the lens at a position of 31.0 cm.


(iii)State the nature of the image formed if the candle flame is further shifted towards the lens.