Physical and Chemical Changes — Science STD 7 — Question

In places of hot climate it is advised that the outer walls of houses be painted white. Explain.

If you leave a piece of iron in the open for a few days, it acquires a film of brownish substance, called rust.
Do you think formation of rust on iron is a chemical change?

Look at the given reaction.
Hydrochloric acid + Sodium hydroxide (base) → Sodium chloride (salt) + Water
Sodium chloride formed in this reaction remains in solution form. Can we get solid sodium chloride from this solution? Suggest a method (if any).

Explain the importance of hygiene during menstruation.

What are these red and blue litmus paper strips made of? Why do they change colour when drops of some samples are put on them?

Can you give me a name? Solve each of the following riddles by writing the name of the organism and its mode of nutrition. One riddle is solved to help you. I am tall but I cannot move. I am green and can prepare my own food. , .

Why are wires not made from coal?

You must be familiar with the following nursery rhymes:

1. ‘Baa baa black sheep, have you any wool.’
2. ‘Mary had a little lamb, whose fleece was white as snow.’

Answer the following:

1. Which parts of the black sheep have wool?
2. What is meant by the white fleece of the lamb?

Why is it important to learn from failed experiments?

What is rusting? How can it be prevented?