Secondary School (English Medium) (5 to 8) कक्षा ७ - CBSE Question Bank Solutions for Science

Place the following statements in a proper order to form a meaningful paragraph.

1. Which in turn decreases the seepage of rain water into the ground.
2. This decreases the open areas like parks and playgrounds.
3. Increasing population create demand for construction of houses, shops, offices, roads and pavements.
4. This results in depletion of water table and creates scarcity of more water.

Paheli wrote a food chain in the following way:

frog → eagle → insects → grass → snake

The chain is not in the correct order. Help her to write the food chain correctly.

Which of the following is a part of inorganic impurities of the sewage?

Why are open drains a concern?

Using the knowledge of acids and bases, write a secret message with the help of baking soda and beet root. Explain how it works.

(Hint: Prepare baking soda solution in water. Use this solution to write the message on a sheet of white paper with a cotton bud. Rub a slice of fresh beetroot over the message.)

Prepare red cabbage juice by boiling a piece of red cabbage in water. Use it as an indicator and test the acidic and basic solutions with it. Present your observations in the form of a table.

Take three glass bottles with wide mouths. Label them A, B, and C. Fill about half of the bottle A with ordinary tap water. Fill bottle B with water which has been boiled for several minutes, to the same level as in A. In bottle C, take the same boiled water and of the same amount as in other bottles. In each bottle put a few similar iron nails so that they are completely under water. Add a teaspoonful of cooking oil to the water in bottle C so that it forms a film on its surface. Put the bottles away for a few days. Take out nails from each bottle and observe them. Explain your observations.

Play with a mirror

Write your name with a sketch pen on a thin sheet of paper, polythene or glass. Read your name on the sheet while standing in front of a plane mirror. Now look at your image in the mirror.

A burning candle in water

Take a shoe box, open on one side. Place a small lighted candle in it. Place a clear glass sheet (roughly 25 cm × 25 cm) in front of this candle figure. Try to locate the image of the candle behind the glass sheet. Place a glass of water at its position. Ask your friends to look at the image of the candle through the sheet of glass. Ensure that candle is not visible to your friends. Your friends will be surprised to see the candle burning in water. Try to explain the reason.

Visit an electric shop. Request an electrician to show you the various types of fuses and MCB and to explain how they work.

The silkworm is (a) a caterpillar, (b) a larva. Choose the correct option

Make sketches of the two stages in the life history of the silk moth which are directly related to the production of silk.

Out of the following, which are the two terms related to silk production?

Sericulture, floriculture, moriculture, apiculture and silviculture

Hints:

(1) Silk production involves cultivation of mulberry leaves and rearing silkworms.

(2) Scientific name of mulberry is Morus alba.

Match the words of Column I with those given in Column II:

Describe the process of neutralization with the help of an example.

Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water.

Two methods by which rusting of iron can be prevented are ______ and ______.

Explain how painting of an iron gate prevents it from rusting.

Explain why rusting of iron objects is faster in coastal areas than in deserts.

The rear view mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/s. The driver sees in his rear view mirror the image of truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be ______.