CBSE Class 7 Science – NCERT Study Materials | Notes

Q1: What is a metal?
A: An element that is usually lustrous, malleable, ductile and a good conductor of heat and electricity.
Q2: What is a non-metal?
A: An element that is usually dull, brittle (if solid) and a poor conductor of heat and electricity.
Q3: Define alloy.
A: A mixture of two or more elements, at least one of which is a metal, made to improve properties.
Q4: What is an ore?
A: A rock from which a metal can be extracted economically.
Q5: What does ‘corrosion’ mean?
A: The gradual destruction of metals through reaction with the environment (e.g., rusting).
Q6: What is rust?
A: Hydrated iron(III) oxide formed when iron reacts with oxygen and water.
Q7: Define ductility.
A: The ability of a metal to be drawn into thin wires.
Q8: What is malleability?
A: The ability of a metal to be hammered into thin sheets without breaking.

Q9: Give one example of a metal with lustre.
A: Copper (also gold, silver).
Q10: Name a sonorous metal.
A: Iron or steel (they ring when struck).
Q11: Why are metals good conductors?
A: Because free electrons in metals carry heat and electric charge easily.
Q12: State one use of the ductility of metals.
A: Making electrical wires from copper.
Q13: Are metals generally hard or soft?
A: Many metals are hard, but some (like sodium) are soft; hardness varies with the metal.
Q14: Can metals be magnetic?
A: Yes, some metals like iron, nickel and cobalt are magnetic.
Q15: What does ‘lustre’ refer to?
A: The shiny appearance of a metal surface.
Q16: Give an example of a light metal used in cooking vessels.
A: Aluminium.
Q17: Why are metals used for making vessels?
A: Because they conduct heat well and are strong.
Q18: What property makes metals suitable for making coins?
A: Durability and malleability.

Q19: Give one example of a non‑metal that is a gas.
A: Oxygen or nitrogen.
Q20: Are non‑metals good conductors?
A: No, most non‑metals are poor conductors of heat and electricity.
Q21: Give one brittle non‑metal.
A: Sulfur (solid sulfur is brittle).
Q22: Name a non‑metal used in pencils.
A: Carbon (as graphite).
Q23: Which non‑metal is essential for respiration?
A: Oxygen.
Q24: Give one non‑metal used in fertilizers.
A: Nitrogen (in compounds like ammonium nitrate).
Q25: Are non‑metals sonorous?
A: No, solids of non‑metals are generally non‑sonorous.

Q26: What forms when magnesium burns in air?
A: Magnesium oxide (white ash).
Q27: Name a metal that reacts violently with cold water.
A: Sodium (also potassium).
Q28: What gas is released when a metal reacts with dilute acid?
A: Hydrogen gas.
Q29: Does copper react with cold water?
A: No, copper does not react with cold water.
Q30: What happens when sulfur burns?
A: It forms sulfur dioxide (a non‑metal oxide).
Q31: Give one example of a metal reacting with oxygen to form oxide.
A: 2Mg + O₂ → 2MgO (magnesium oxide).
Q32: Why do some metals not react with acids?
A: Because they are less reactive and do not displace hydrogen from acids (e.g., copper).
Q33: What is observed when zinc reacts with dilute hydrochloric acid?
A: Effervescence due to hydrogen gas; zinc dissolves forming zinc chloride.
Q34: Name a non‑metal that reacts with oxygen to form an acidic oxide.
A: Sulfur (forms sulfur dioxide).
Q35: What do metals form on reacting with oxygen?
A: Metallic oxides.
Q36: Give one example where metal + acid → salt + hydrogen.
A: Zn + 2HCl → ZnCl₂ + H₂.

Q37: Name a metal that is very reactive.
A: Potassium (also sodium, calcium).
Q38: Name a metal that is least reactive.
A: Gold (also silver).
Q39: What is the use of a reactivity series?
A: To compare how easily metals lose electrons and react with substances like water and acids.
Q40: Which metal among sodium and copper is more reactive?
A: Sodium is more reactive than copper.
Q41: Why is gold used for jewellery despite being expensive?
A: Because it is very unreactive and does not corrode or tarnish easily.

Q42: What three things are needed for rusting?
A: Iron, oxygen and water.
Q43: Does saltwater speed up rusting?
A: Yes, saltwater speeds up rusting by acting as an electrolyte.
Q44: Name one method to prevent rusting.
A: Painting (others: galvanisation, oiling, alloying).
Q45: What is galvanisation?
A: Coating iron or steel with zinc to protect it from rusting.
Q46: How does zinc protect iron in galvanisation?
A: Zinc acts as a sacrificial metal and corrodes in place of iron.
Q47: Why is oiling used on machine parts?
A: To form a protective layer that prevents moisture from reaching metal surfaces.

Q48: Give one example of an alloy and its use.
A: Steel (iron + carbon) — used in construction and tools.
Q49: What is a native metal? Give an example.
A: A metal found in nature in free state; example: gold.
Q50: Name one metal and one non‑metal used in daily life.
A: Metal: Copper (wires). Non‑metal: Oxygen (breathing), Carbon (pencils).

Science — Chapter 4: The World of Metals and Non-metals