Q13 of 33 Page 1

“pH has a great importance in our daily life” explain by giving three examples.

Three examples are

a. The pH of soil plays an important role in the growth of plants. Plants grow well in specific pH range.


b. In our stomach pH should be maintained. Decreased pH value increases acidic nature and we suffer from a condition called acidity.


c. Water bodies should have constant pH range, as any changes in this range will affect aquatic life.


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11

How do Mendel’s experiments show that traits may be dominant or recessive?

 12

Rohit focused the image of a candle flame on a white screen using a convex lens. He noted down the position of the candle, screen and lens as under:

Position of candle = 26.0 cm


Position of convex lens = 50.0 cm


Position of screen = 74.0 cm


i) What is the focal length of the convex lens?


ii) Where will the image be formed if he shifts the candle towards the lens at a position of 38 cm?


iii) Draw a ray diagram to show the formation of the image in case (ii) as said above?

 13

A compound which is prepared from gypsum has the property of hardening when mixed with a proper quantity of water. Identify the compound and write its chemical formula. Write the chemical equation for its preparation. Mention any one use of the compound.

 14

Why are fossils considered important in the study of evolution? Explain two ways by which age of fossils can be estimated.