Science 3 Marks Question

In the summer holidays, Karan went to Rann of Kutch In Gujarat with his parents. Karan was aware that in the coastal regions of India especially in the Rann of Kutch common salt is obtained from sea water. Karan was very excited to see that place. He requested his father that he want to see the process of obtaining salt from sea. His father helped him and they went to see the place where common salt was collecting. And he also explained the whole process. Karan was very happy to see the process.
Now, answer the following questions.
(i) How the crystals of common salt obtained from sea water?
(ii) Name the process by which salt is collected from sea water?

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 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
(i) Why his cycle gets rusted?
(ii) What do you mean by rusting of iron?

Give an example of a chemical reaction for each of the following situations
(i) A change in colour is observed.
(II) A gas is evolved.
(III) Sound is produced.

Give two examples for each of the following cases
(i) Physical changes, which are reversible.
(ii) Physical changes, which are not reversible.
(iii) Chemical changes

Amit dissolved sugar in water and observed the change. His friend Raj took a little sugar in a spatula and directly heated it on a bunsen burner on a high flame.
Answer the following questions.
(i) Which type of changes is observed by the Amit? Is it reversible or irreversible?
(ii) Who of the two will observe chemical change?

Abhi burned a substance X over the candle flame and white dazzling light is observed. Also white powdery ash left behind. He mixed the white ash formed with small amount of water. Then he dipped red and blue litmus papers into the solution one by one.
(i) Identify the substance X.
(ii) Which substance is formed after substance X gets burnt?
(iii) What is the nature of solution formed after mixing the white ash into the water acidic or basic?

Write the differences between physical and chemical changes.

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

When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.

Classify the changes involved in the following processes as physical or chemical changes.
(a) Photosynthesis
(b) Dissolving sugar in water
(c) Burning of coal
(d) Melting of wax
(e) Beating aluminium to make aluminium foil
(f) Digestion of food

Explain, how rusting damages iron objects?

What happens when magnesium oxide is dissolved in water? Write a word equation for this process. Name the type of change which takes place.