CBSE Guess > Papers > Question Papers > Class X > 2008 >Science > Science Theory

(ii) The scum (or precipitate) formed by the action of hard water on soap sticks to the clothes being washed and it interferes with the cleaning ability of soap. This makes the cleaning of clothes difficult.

or

Complete the following equations

(i)

(ii)

(iii)

Write the name of the following :
(i) CH₃CH₂COOH
(ii) CH₃CH₂Br
(iii) Draw the electron dot structure of ethene (C2H4).

Ans.

(b)

1. CH₃CH₂COOH Propanoic Acid
2. CH₃CH₂Br Bromo ethane

(c) Electron dot structure of ethene (C₂H₄ ).

Section B

Q.17. What is the role of saliva in the digestion of food?

Ans. The saliva contains an enzyme called salivary amylase which digests the starch present in food into sugar. Thus, the digestion of starch begins in the mouth.

Q.18. Why is the use of iodised salt advisable?

Ans. The use of iodised salt is advisable because iodine is required by the thyroid gland to make thyroxine hormone. Iodised salt contains appropriate amount of (potassium iodide). Iodised salt can provide all the iodine needed by thyroid gland to make sufficient thyroxine for our body. So, it helps in preventing goitre.

Science 2008 Question Papers Class X
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