CBSE 10th Chemistry | Chemical Reactions and Equations -NCERT Questions with Answers

Chemical Reactions and Equations -NCERT Questions with Answers

Question 1. Which of the statements about the reaction below are incorrect?

2PbO(s) + C(s) clip_image0022Pb(s) + CO2(g)

(a) Lead is getting reduced,

(b) Carbon,dioxide is getting oxidised.

(c) Carbon is getting oxidised.

(d) Lead oxide is getting reduced

(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all


The statements (a) and (b) are incorrect because PbO is getting reduced, not Pb, similarly C is getting oxidized not CO2.

Question 2. Fe2O3 + 2Al clip_image002[1]Al2O3 + 2Fe

The above reaction is an example of a

(a) combination reaction

(b) double displacement reaction

(c) decomposition reaction,

(d) displacement reaction.



(d) The given reaction is an example of displacement reaction as in this reaction Al displaces, Fe from Fe2O3.

Question 3. What happens when dilute hydrochloric acid is added to iron fillings? tick the correct answer.

(a) Hydrogen gas and iron chloride are produced

(b) Chlorine gas and iron hydroxide are produced

(c) No reaction takes place

(d) Iron salt and water are produced



(a) Fe(s) + 2HCl(aq) clip_image002[2] FeCI2(aq) + H2(g)

Question 4. What is a balanced chemical equation? Why should chemical equations be balanced?


Balanced chemical equation: – A chemical equation is said to be balanced if the number of atoms of each element participating in the reaction are equal on both side of the equation.

The chemical reaction should be balanced because law of conservation of mass holds good which states that “in a chemical reaction total mass of the reactant must be equal to the total mass of the product”.

Quiestion 5. Translate the following statements into chemical equations and then balance them.

(a) Hydrogen gas combines with nitrogen to form ammonia.

(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.

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

(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.


(a) N2(g) + 3H2(g) clip_image002[3]2NH3(g)

(b) 2H2S(g) +3O2(g) clip_image002[4]2H2O(l) +2SO2(g)

(c) 3BaCl2(aq) + Al2 (SO4)3(s)clip_image002[5] 3BaSO4(s) + 2AlCl3(aq)

(d) 2K(s) + 2H2O(l) clip_image002[6] 2KOH(aq)+H2(g)

Question 6. Balance the following chemical equations.

(a) 2HNO3 + Ca(OH)2 clip_image002[7] Ca(NO3)2 + H2O

(b) NaOH + H2SO4 clip_image002[8] Na2SO4 + H2O

(c) AgNO3 + NaCl clip_image002[9]AgCl + NaNO3.

(d) BaCl2 + H2SO4 clip_image002[10]BaSO4 + HCl


(a) 2HNO3 + Ca(OH)2 clip_image002[11] Ca(NO3)2 + 2H2O

(b) 2NaOH + H2SO4 clip_image002[12] Na2SO4 + 2H2O

(c) AgNO3 + NaCl clip_image002[13] AgCl + NaNO3

(d) BaCl2 + H2SO4 clip_image002[14]BaSO4 + 2HCl

Question 7. Write the balanced chemical equations for the following reactions.

(a) Calcium hydroxide + Carbon dioxideclip_image002[15] Calcium carbonate + water

(b) Zinc + Silver nitrate clip_image002[16] Zinc nitrate + Silver

(c) Aluminium + Copper chloride clip_image002[17] Aluminium chloride + Copper

(d) Barium chloride + Potassium sulphate clip_image002[18]Barium sulphate + Potassium chloride


(a) Ca(OH)2 + CO2 clip_image002[19] CaCO3 + H2O

(b) Zn+2AgNO3clip_image002[20] Zn(NO3)2 + 2Ag

(c) 2Al + 3CuCl2 clip_image002[21]2AlCl3 + 3Cu

(d) BaCl2 + K2SO4clip_image002[22] BaSO4+2KCl

Question 8. Write the balanced chemical equation for the following and identify the type of reaction in each case.

(a) Potassium bromide(aq) + Barium iodide(aq) clip_image002[23] Potassium iodide(aq) + Barium bromide(aq)

(b) Zinc carbonate(s) clip_image002[24] Zinc oxide(s) + Carbon dioxide(g)

(c) hydrogen(g) + Chlorine(g) clip_image002[25] Hydrogen chloride(g)

(d) Magnesium(s) + Hydrochloric acid(aq) clip_image002[26] Magnesium chloride(aq) + Hydrogen(g)


(a) 2KBr(aq) + Bal2(aq) clip_image002[27] 2KI(aq) + BaBr2(aq)

(b) ZnC03(s) clip_image002[28] ZnO(s) + CO2(g)

(c) H2(g) + Cl2(g) clip_image002[29] 2HCl(g)

(d) Mg(s) + 2HCl(aq) clip_image002[30] MgCl2(aq) + H2(g)

Question 9. What does one mean by exothermic and endothermic reaction? Give examples.


Exothermic reaction: – Those reactions which occur with evolution of heat are exothermic reactions. e.g.

2NaOH(aq) + H2SO4(aq) clip_image013Na2SO4(aq) + 2H2O(l) + Q

Enothermic reaction: – Those reactions which require heat to occur are endothermic reactions, e.g.

2Pb(NO3)2(s) + Q clip_image002[31] 2PbO(s) + 4NO2(g) + O2(g)

Question 10. Why is respiration considered an exothermic reaction? Explain.


During respiration oxidation of glucose occur which produce heat energy.

Question 11. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.


During decomposition reaction a single reactant decompose to form two or more products, whereas in combination two or more reactant react to form a single product, e.g.

N2 + 3H2 clip_image002[32]2NH3 (Combination reaction.)

2H2O image 2H2 + O2 (Decomposition reaction.)

Question 12. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.




Question 13. What is the difference between displacement and double displacement reactions? Write equations for these reactions.


Displacement reaction: In this reaction an element which is more active displaces the other element which is less active from its salt solution.

e.g. Fe(s) + CuSO4(aq) clip_image002[33] FeSO4(aq) + Cu(s)

Double displacement reaction: In this reaction exchange of ions between two reactants take place, e.g.

BaCl2(aq) + Na2SO4(aq) clip_image002[34] BaSO4(s) + 2NaCl(aq)

Question 14. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.


Cu(s) + 2AgNO3(aq) clip_image002[35] Cu(NO3)2(aq) + 2Ag(s)

Question 15. What do you mean by a precipitation reaction? Explain by giving examples.


Those reactions which produce an isoluble product or precipitate are known as precipitation reaction. e.g.AgNO3(aq) + NaCl(aq) clip_image002[36] AgCl(s) +NaNO3(aq)

Question 16. Explain the following in terms of gain or loss of oxygen with two examples each.

(a) Oxidation

(b) Reduction


Oxidation: Oxidation involve addition of oxygen e.g.

C + O2 clip_image002[37] CO2, C is oxidised to CO2.

N2 + O2 clip_image002[38] 2NO, N2 is oxidised to NO.

Reduction: Reduction involve removal of oxygen, e.g.

C + H2O clip_image002[39] CO + H2, H2O is reduced to H2.

CuO + H2 clip_image002[40] Cu + H2O, CuO is reduced to Cu.

Question 17. A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.



Question 18. Why do we apply paint on iron articles?


To prevent iron articles from rusting, we apply paint on it, by which iron does not come in contact with air and moisture which cause rusting.

Question 19. Oil and fat containing food items are flushed with nitrogen. Why?


When the oil and fat containing food is surrounded by unreactive gas nitrogen, there is no oxygen to cause its oxidation and make it rancid.

Question 20. Explain the following terms with one example each.

(a) Corrosion

(b) Rancidity



Corrosion: It is a process in which metals are eaten up gradually by the action of air, moisture or a chemical on their surface.

Rancidity: When fats and oil containing food are oxidised with air or oxygen, their smells and tastes changes. This process is called rancidity.


CBSE 9th Physics | Motion NCERT Problems with Solutions- Part 2

Motion NCERT Problems with Solutions- Part 2

Motion is a very important topic of Physics. Here are Motion NCERT Problems with Solutions for your practice

Problem 1. A motorboat starting from rest on a lake accelerates in a straight line at a constant rate of 3.0 m s-2 for 8.0 s . How far does the boat travel during this time?



Problem 2. Fig. shows the distance-time graph of three objects A, B and C. Study the graph and answer the following questions:


Which of the three is traveling the fastest?

Are all three ever at the same point on the road?

How far has C traveled when B passes A?

How far has B traveled by the time it passes C?



(ii) No, all three do not meet at any point on the road,

(iii) When B passes A at point N (at 1.2 hours), C is at a distance of approximately 8 km from

the origin O.

(iv) B passes C at 0.7 hours. During this time B covers distance of 6 km.

Problem 3. A ball is gently dropped from a height of 20 m. If its velocity increases uniformly at the rate of 10 ms-2, with what velocity will it strike the ground? After what time will it strike the ground?



Problem 4. The speed-time graph for a car is shown is Fig.


(a) Find how far does the car travel in the first 4 seconds. Shade the area on the graph that represents the distance traveled by the car during the period.

(b) Which part of the graph represents uniform motion of the car?



(a) On horizontal axis, 5 small divisions = 2 s On vertical axis, 3 small divisions = 2 m/s

clip_image030[1] Area of 15 small squares

= 2 s x 2 m/s = 4m

Area of 1 small square =4/15m

Total area under the speed-time graph from time 0 to 4 s

= 57 small squares + 1/2 x 6 small squares

= 60 small square

Distance traveled by the car in first 4 seconds

= Area under the speed-time graph from 0 to 4 s

= 60 small squares

= 60 x 4/15 m

= 16 meter.


(b) After 6 s, the car has a uniform motion for straight part of graph BC.


Problem 5. State which of the following situations are possible and give an example for each of these:

(a) an object with a constant acceleration but with zero velocity.

(b) an object moving in a certain direction with an acceleration in the perpendicular direction.



(a) Yes, a body can have acceleration even if its velocity is zero. When a body is thrown

up, at highest point its velocity is zero but it has acceleration equal to acceleration due to gravity.

(b) Yes, when an object moves on a circular path, it has centripetal acceleration which is perpendicular to displacement.

Problem 6. An artificial satellite is moving in a circular orbit of radius 42250 km. Calculate its speed if it takes 24 hours to revolve around the earth.