Forests: Our Lifeline — Science STD 7 — Question

Three test tubes A, B and C are taken as shown in figure below. Red litmus paper was dipped in all three test tubes to test which solution is basic in nature. Identify in which test tube the red litmus paper will change its colour to blue?

Give the main causes of water scarcity in our country.

Describe the steps involved in getting clarified water from wastewater.

Rahul was a student of Class VII. His father purchased a new bicycle for him on his birthday. After few months, he found that the cycle chain and even the handle gets rusted. His father advised him to apply a coating of paint to the cycle and not to keep it in the open in future.
Now, answer the following Questions:

1. Why his cycle gets rusted?
2. What do you mean by rusting of iron?
3. What values are shown by Rahul’s father?

Draw a pictorial presentation of the process of rusting and explain the chemical changes involved.

Like humans and animals, transportation of water, mineral and nutrients also take place in plants. How?

What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas?

What is neutralisation? Give examples of neutralisation in daily life.

If you leave a piece of iron in the open for a few days, it acquires a film of brownish substance, called rust.
(a) Do you think rust is different from iron?
(b) Can you change rust back into iron by some simple method?
(c) Do you think formation of rust from iron is a chemical change?
(d) Give two other examples of a similar type of change.