In this article, you will find the answers and detailed solutions for the NCERT questions of class 7 science chapter 4 "The World of Metals and Non-metals".
The World of Metals and Non-metals - NCERT Solutions
1. Which metal is commonly used to make food packaging materials as it is cheaper, and its thin sheets can be folded easily into any shape?
(i) Aluminium
(ii) Copper
(iii) Iron
(iv) Gold
Ans: (i) Aluminium
2. Which of the following metal catches fire when it comes in contact with water?
(i) Copper
(ii) Aluminium
(iii) Zinc
(iv) Sodium
Ans: (iv) Sodium
3. State with reason(s) whether the following statements are True [T] or False [F].
(i) Aluminium and copper are examples of non-metals used for making utensils and statues.
(ii) Metals form oxides when combined with oxygen, the solution of which turns blue litmus paper to red.
(iii) Oxygen is a non-metal essential for respiration.
(iv) Copper vessels are used for boiling water because they are good conductors of electricity.
Ans:
(i) False [ F ]: Aluminium and copper are metals, not non-metals.
(ii) False [ F ]: Metal oxides are basic; their solutions turn red litmus paper to blue.
(iii) True [ T ]: Oxygen is a non-metal vital for breathing.
(iv) False [ F ]: They are used because they are good conductors of heat, though they also conduct electricity.
4. Why are only a few metals suitable for making jewellery?
Ans: Most metals are too reactive or dull. Suitable metals like gold and silver are chosen because they are lustrous (shiny) and highly unreactive, so they don't tarnish easily.
5. Match the uses of metals and non-metals given in Column I with the jumbled names of metals and non-metals given in Column II.
Ans:
(i) Used in electrical wiring — (c) COPPER (P E P O R C)
(ii) Most malleable and ductile — (e) GOLD (O G D L)
(iii) Living organisms cannot survive without it — (a) OXYGEN (E N X Y G O)
(iv) Plants grow healthy with these fertilisers — (d) NITROGEN (T E N G O I N R)
(v) Used in water purification — (b) CHLORINE (N E C O H I R L)
6. What happens when oxygen reacts with magnesium and sulfur. What are the main differences in the nature of products formed?
Ans:
- Magnesium: Reacts with oxygen to form Magnesium Oxide (MgO), which is basic in nature.
- Sulfur: Reacts with oxygen to form Sulfur Dioxide (SO2), which is acidic in nature.
- Main Difference: Metal oxides (Magnesium) are basic, while non-metal oxides (Sulfur) are generally acidic.
7. Complete the following flow chart:
Ans:
8. You are provided with the following materials. Discuss which material would be your choice to make a pan that is most suitable for boiling water and why?
Ans: Copper is the best choice to make a pan. It is an excellent conductor of heat. It will allow water to boil quickly. Copper is also durable enough to tolerate high temperatures without melting (unlike plastic or wood).
9. You are provided with three iron nails, each dipped in oil, water and vinegar. Which iron nail will not rust, and why?
Ans: The nail dipped in oil will not rust. Oil make a protective layer that prevents oxygen and moisture from the air from coming into contact with the iron. Without air and moisture, rusting will not happen.
10. How do the diff erent properties of metals and non-metals determine their uses in everyday life?
Ans:
- Metals: Their malleability allows them to be beaten into sheets (aluminum foil) and their ductility allows them to be drawn into wires (copper wiring).
- Non-metals: Their property as insulators makes them useful for tool handles (plastic/wood) to prevent heat or electric shocks.
11. One of the methods of protecting iron from getting rusted is to put a thin coating of zinc metal over it. Since sulfur does not react with water, can it be used for this purpose? Justify your answer.
Ans: No. Sulfur cannot protect iron from rusting. Sulfur does not react with water, it is brittle and cannot form a rigid and strong layer like zinc (galvanization). It would simply peel off, leaving the iron exposed.
12. An ironsmith heats iron before making tools. Why is heating necessary in this process?
Ans: Ironsmith heats iron before making tools to make it more malleable. At high temperatures, iron becomes soft and easy to hammer into different shapes without breaking.