Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium suphide
(iv) magnesium hydroxide

Convert into mole.

(a) 12 g of oxygen gas
(b) 20 g of water
(c) 22 g of carbon dioxide.

Why is the atmosphere essential for life?

What happens to the force between two objects, if
(i) the mass of one object is doubled?
(ii) the distance between the objects is doubled and tripled?
(iii) the masses of both objects are doubled?

You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?

Why are we normally advised to take bland and nourishing food when we are sick?

Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?

In which of the following case do you think the long-term effects on your health are likely to be most unpleasant?
  •  if you get jaundice,
  •  if you get lice,
  •  if you get acne.

Why?

Name the technique to separate

(i) butter from curd,
(ii) salt from sea-water,
(iii) camphor from salt.

What are the immunisation programmes available at the nearest health centre in your locality? Which of these diseases are the major health problems in your area?

A stone is released from the top of a tower of height 19.6 m. Calculate its final velocity.

Why is it not possible to see an atom with naked eyes?

Name the technique to separate

(i) butter from curd,
(ii) salt from sea-water,
(iii) camphor from salt.

Convert into mole.

(a) 12 g of oxygen gas
(b) 20 g of water
(c) 22 g of carbon dioxide.

Explain the following giving examples.

(a) saturated solution
(b) pure substance
(c) colloid
(d) suspension

A pair of bullocks exerts a force of 140 N on a plough. The field being ploughed is 15 m long. How much work is done in ploughing the length of the field?

Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?

Name the regions in which parenchyma tissue is present.

Why is the weight of an object on the moon 1/6th its weight on the earth?

To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature.

If bromine atom is available in the form of, say, two isotopes ⁷⁹₃₅ Br (49.7%) and ⁸¹₃₅ Br (50.3%), calculate the average atomic mass of bromine atom.