Physical and Chemical Changes Test - 3

Lactic acid bacteria (LAB) like lactobacillus are added to milk. It converts lactose sugar of milk into lactic acid. Lactic acid causes coagulation and partial digestion of milk protein casein. Milk is changed into curd, yoghurt and cheese.

A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light. When we look towards the sun at sunset, we see red and orange colors because the blue light has been scattered out and away from the line of sight.

Hence, scattering is the characteristic property of light which is responsible for the blue colour of the sky.

According to this question the correct option will be ‘C’ because Lime water turns milky when you pass carbon dioxide through it because a reaction that produces a white precipitate takes place. When you pass carbon dioxide through this solution, the two compounds carbon dioxide and calcium hydroxide  will react to form white and insoluble calcium carbonate which precipitates out of the solution.

According to this question the correct option will be ‘C’ because When we put an iron nail in a copper sulphate solution, we find the blue color of the solution changes to green.

According to this question, the correct option will be ‘A’ as the tearing of books pages is a physical and irreversible change. As in the tearing of paper, no new substance is formed.

According to this question the correct option will be ‘C’ because Composition of the iron pillar make it resistant of rusting. When it has not rusted after such a long period.

According to this question the correct option will be ‘A’ as  Flammability is a chemical property because combustion is a chemical change. A chemical change is a process in which one or more substances are converted into one or more new substances with different properties. Gasoline is highly flammable. When it burns, it is converted into carbon dioxide and water.

According to this question the correct option will be ‘A’ because Heat may be given out as well as absorbed during chemical reactions.

According to this question the correct option will be ‘B’ because Iron gate does not need to be protected from sun. Paints cannot avoid dust. To prevent rusting of iron gate, we do paint on it. Painting makes it beautiful

According to this question the correct option will be ‘B’ because except the option B that is “Heating of iron” in all other reactions, there is molecule changes and one object convert in to other object hence these are chemical changes process while heating of iron is physical change process.