Science 'N' us-5 final - School Books Publishers India

2. Explain the composition of air.Ans. Air present in the troposphere is a mixture of many gases. Mainly, aircontains nitrogen, oxygen, carbon dioxide, water vapour and othergases like argon, neon, helium, ozone, hydrogen, etc.3. Give one use of :(a) neon (b) carbon dioxide (c) heliumAns. (a) Neon is used for preparing brightly coloured advertising lights.(b) Carbon dioxide is needed by the plants to carry out photosynthesisto make food for themselves and for all living world.(c) Helium is used for filling balloons.4. Which processes are used to remove the soluble impurities fromthe water?Ans. We removed the soluble impurities from the water by following methods :(i) By evaporation : Take some tablespoons of salt and dissolve it inwater. Now pour this salt solution into a flat dish. Boil the water till allthe water evaporates.After sometime you will find that salt settled at the bottom of the dish.This way we can separate salt and other soluble impurities from water.Pure water can be obtained by collecting the water vapours and thencondensing them.(ii) By distillation : In this process of evaporation, water is heated toseparate the soluble substances, such as sugar as salt. In this process waterevaporates in the form of water vapour and gets collected in other jarleaving the crystals of soluble substance in the dish. Thus, the process inwhich water on heating is converted into water vapours and pure water iscollected by cooling these water vapours, is called distillation.5. Explain the process of filtration of water.Ans. We can remove the insoluble impurities by passing the water through afilter paper. This helps to remove very fine suspended impuritiespresent in the water.6. What is air pollution? Write two ways to control it.Ans. Air is said to be polluted if it contains substances that are harmful tohuman beings animals, plants, etc.1. Factories should be set up on the outside of the city.2. We should use eco-friendly fuels like CNG (Compressed Natural Gas).B. Choose the correct word from side box and fill in the blanks :1. Atmosphere of the earth is divided into four layers. distillation2. 78% of air is nitrogen. soluble3. Three types of impurities, soluble, insoluble and germs fourare found in the water.germs4. To remove the soluble impurities from the water, stratosphereevaporation and distillation methods are used.insoluble5. Ozone gas is present in stratosphere layer. evaporationnitrogenHorizon Press121Science 'n' Us - 1 to 5