NCERT Class 10 Chapter 1 Chemical Reaction and Equation CBSE Board Sample Problems Long Answer (For CBSE, ICSE, IAS, NET, NRA 2022)

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What is meant by ‘rusting’ ? With labeled diagrams, describe an activity to find out the conditions under which iron rusts.


Rusting is corrosion of iron to a brown flaky substance in the presence of moist air. Activity to find out the conditions under which iron rusts:

  • Take three test tubes and place clean iron nails in each of them.
  • Label these test tubes as A, B and C.
  • Pour some water in test tube A and cork it.
  • Pour boiled distilled water in test tube B, add about 1 mL of oil and cork it. The oil will float on water and prevent air from dissolving in water.
  • Put some anhydrous calcium chloride in test tube C and cork it. Anhydrous calcium chloride will absorb the moisture, if any, from the air.
  • Leave the three test tubes for a few days and then observe. Observation: The iron nails in test tube a rusts. In test tubes B and C, no rusting occurs.

Conclusion: Both air and moisture are necessary for rusting of iron.


When hydrogen is passed over copper oxide, copper and steam are formed. Write a balanced chemical equation for this reaction and state which of the chemicals are

i) Elements

ii) Compounds

iii) Reactants

iv) Products

v) Metals

vi) Non-metals


Balanced Chemical Equation

i) Elements: copper, hydrogen, oxygen

ii) Compound: Water, Copper oxide

iii) Reactants: Copper oxide and hydrogen gas

iv) Products: Copper and water

v) Metal: copper

vi) Non-Metal: Hydrogen and oxygen


What happens when silver chloride decomposes in presence of sunlight? Write the chemical reaction involved identify the type of reaction. What is the application of this reaction?


It is a photolytic decomposition reaction

The application of this reaction is in black and white photography.


On heating blue coloured powder of copper nitrate in a boiling tube, copper oxide oxygen gas and a brown gas X is formed.

a) Write a balanced chemical equation of the reaction.

b) Identify the brown gas X evolved.

c) Identify the type of reaction.

d) What could be the pH range of aqueous solution of the gas X?



b) The brown gas is nitrogen dioxide

c) It is a decomposition reaction.

d) is oxide of non metal . On dissolving in water it will produce an acidic solution, So the pH of solution will be less than 7.


(a) . Hydrous ferrous sulphate crystals are heated in a boiling tube for few seconds.

Water droplets are seen in the inner sides of test tube and the colour of the crystals changes. On continuous heating a colourless gas X with smell of burning sulphur is evolved and a residue Y is obtained.

(i) What is the colour of the crystals before and after mild heating?

(ii) Identify the gas X and the residue Y formed.

(iii) Write the balanced chemical equation for the above reaction.

(b) Write balanced chemical equations for the following reactions.

(i) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.

(ii) Sodium metal reacts with water to give sodium hydroxide and hydrogen gas.


a) . Green, White

(ii) X is Sulphur dioxide () or Sulphur trioxide and Y is Ferric oxide ()


(b) . i)



(a) Write a balanced chemical equation for each of the following types of chemical reactions:

(i) Displacement reaction

(ii) Double displacement reaction

(iii) Photolytic decomposition reaction

(b) Consider the chemical equation given below and answer the questions that follow:

(i) Name the substance which is getting oxidized and the substance which is getting reduced.

(ii) Name the oxidizing and the reducing agent.





(b) (i) Hydrogen, Copper oxide.

(ii) Copper oxide, Hydrogen


What are fossils? How are they formed? Describe in brief two methods of determining the age of fossils. State any one role of fossils in the study of the process of evolution



  • Fossils are preserved remains or impressions of pre- historic organisms in the different strata of the earth՚s crust OR Fossils are dead remains of animals and plants from remote past.
  • Fossils are formed when dead organisms are not completely decomposed. The organisms may get trapped in resins of tree, lava of volcanoes or hot mud which when hardens, retains the animal՚s parts thus, forming fossils.
  • Two methods of determining the age of fossils:
    • Relative method: By estimating the age of the layer of earth՚s crust where the fossil is found. Fossils near the surface are recent and those in the deeper layers are more ancient.
    • Radio-carbon dating method: By detecting the ratio of different isotopes of carbon in the fossils.
    • Fossils help in determining the connecting links between various groups and their origin from their primitive ones. e. g. , Archaeopteryx.


A metal X is found in the form of ribbon in the chemistry lab. It burns in the presence of oxygen with a bright dazzling light to form a white solid Z.

a) Identify X and Z

b) Write a balanced chemical equation for the reaction and name the type of reaction.

C) What product would be formed if X is made to react with Nitrogen?


a) X - Magnesium Z - Magnesium Oxide

b) (1) Combination Reaction (1)

C) Magnesium Nitride (1)

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