CBSE class 10 science most important questions and answers -Part 3 - Future Study Point

CBSE class 10 science most important questions and answers -Part 3

CBSE class 10 science most important questions and answers -Part 3

Here, CBSE class 10 science most important questions and answers -Part 3 for 2020-21 CBSE Board part III published by Future Study Point are presented for the students of 10  class who are going to appear in the 2021-22 CBSE board exam.  CBSE class 10 science most important questions and answers for 2021-22 board-III are designed by the expert of the subject and their answers are readily explained in an ordered way.


 CBSE class 10 science most important questions and answers for 2020-21 board-III are designed as per the updated syllabus of CBSE, so you need not to have any kinds of doubt in the selections of the questions. The most important questions of science for class 10 are taken from the last year’s science question papers of class 10, these most important questions of science are the questions of last year’s questions papers of class 10 science which are asked frequently,so the students are required to pay special attention to the solutions of these questions for achieving maximum percentage in a science subject.

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  • Helpful to get additional marks in science

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CBSE class 10 science most important questions and answers -Part 3

Q1. Write a balanced chemical equation for the reactions that take place during respiration. Identify the type of combination reaction that takes place during this process and justifies the name. Give one more example of this type of reaction.

Ans. The respiration process is a combination reaction in which oxygen inhaled by us reacts with the glucose which exists in each cell of the organism because carbohydrate is taken by us ultimately is broken down into glucose. Oxygen combined with this glucose molecule produces carbon dioxide, water, and energy in the form of ATP. The respiration process is given by a chemical equation as follows.

The type of reaction is exothermic because with the products, energy is also released.

Another example of an exothermic chemical reaction is calcium oxide combines with water releases calcium hydroxide along with heat energy.

Note-Many of the students may have doubts that respiration reaction is called here a combination reaction, if  we explain glucose is broken down into carbon dioxide and water then it can be assumed decomposition reaction but from another angle, you say that glucose combines with oxygen releases main product carbon dioxide along water and heat then it can be called combination reaction.It is up to illustration to assume respiration reaction as a combination or decomposition reaction.

Q2. A small amount of quick lime is added to the water in a beaker.

(a)Name and define the type of reaction that has taken place.

(b) Write a balanced chemical equation for the above reaction. Write the chemical name of the product obtained.

(c) State two observations that you will make in the reaction.

Ans. (a) The type of chemical reaction is a combination reaction and a subtype of this reaction is an exothermic reaction because heat is evolved during the reaction, the combination reaction is the type of chemical reaction in which two substances react together forms single substance.

(b) The reaction when quick lime is added to water is shown bellow.


Calcium oxide     Calcium hydroxide

The chemical name of the product obtained i.e slaked lime or lime water is Calcium hydroxide.

(C) Two observations are seen during this reaction are the following.

(i) A hissing sound is emitted during the reaction.

(ii) A large amount of heat is produced during chemical reaction.

Q3.On heating green coloured crystals, a gas with a characteristic
odour of burning sulphur evolves and the colour of crystals change.

(i) Name the gas evolved with its chemical formula.
(ii) Identify the green crystals.

Ans. (i and ii) Green coloured crystals are of hydrated ferrous sulphate i.e FeSO4.7H2O When it is heated changed into anhydrous ferrous sulphate(white colour) thereby it is broken down into ferrous oxide(brown colour), sulphur dioxide and sulphur trioxide,a gas with a characteristic odour of burning sulphur evolves is SO2.

During the reaction, the so formed SO3(sulphur trioxide) is a gas found in solid-state in room temperature.

Q4.“Combination reaction is the reverse of decomposition reaction”. Justify this statement with the help of appropriate chemical equation for each.

Ans. The combination reaction is in which two or more than two compounds or elements form a single compound. As an example, carbon and oxygen combine together forms carbon dioxide.

The decomposition reaction is exactly opposite to the combination reaction because in it one compound breaks down into two or more than two compounds. As an example calcium carbonate, when heated converted into calcium oxide and CO2 .


Q5 Naman and Raghav perform an experiment in which they mix concentrated sulphuric acid with water. Naman mixes water to acid and Raghav mixes acid to water slowly with constant stirring. Mention the suitable reason for selecting the one which you find is a correct method and discarding the one which is wrong.

(a) Compare the properties of a typical metal and a non-metal on the basis of the following :

(i) Nature of the oxide formed by them

(ii) Conductivity

(b) Name a non – metal which is lustrous and a metal which is liquid at room temperature.

Ans. When acid and water are mixed together ions are formed in which a lot of heat releases, in other words, it is an exothermic reaction.

The way of Naman mixing water to acid is quietly wrong, in this way a large amount of heat will be generated, In this method, it takes more time to dilute the acid,initially, there is less water to react with larger proportion of sulphuric acids so the excess amount of heat boils the solution which may splash out of the container harming the person doing this practice and the person near about him.

Raghav mixes acid to water with stirring the whole mixture is the right way of diluting the acid,  the reaction is slower than the reaction occurs when water added to acid because in this case, little acid reacts with more water, so the heat generated will be lesser.

Ans.(a) (i) The oxides are formed as a result of a combination of non-metals or metals with oxygen.

Non-Metalic oxide – These are generally gases in room temperature, the few examples are given below.

Generally, the solution of non-metallic oxide with water is acidic in nature, it is that’s why acid rain is caused by the reaction of SO2 with water forming sulphuric acid and reaction of NO2 with water forming HNO3 acid.

Metallic oxide – The metallic oxide may be either of basic in nature or it may have both characters of basic as well as of acidic, these are formed when metal combines with oxygen.

The sodium oxide reacts with HCl produces salt shows its basic nature while aluminum oxide reacts with acids as well as with base produces salts of a different kind which shows nature of aluminum oxides basic as well as acidic in nature such oxides which have basic and acidic nature known as amphoteric oxides.

(ii) Atoms of metals are not bounded by any bonds like covalent or ionic bonds like non-metals, so their electrons are free to move within the metal which causes them to be a conductor of heat and electricity.  While electrons in non-metals are bounded by the strong electrostatic force exerted by a covalent or ionic bond making them a bad conductor of heat and electricity.

(b) Graphite is the only non-metal which is lustrous and mercury is the only metal that is found in the liquid state at room temperature.

Click the link for more most important questions of class 10 science with answers.

NCERT Solutions of Science and Maths for Class 9,10,11 and 12

NCERT Solutions for class 9 maths

Chapter 1- Number System Chapter 9-Areas of parallelogram and triangles
Chapter 2-Polynomial Chapter 10-Circles
Chapter 3- Coordinate Geometry Chapter 11-Construction
Chapter 4- Linear equations in two variables Chapter 12-Heron’s Formula
Chapter 5- Introduction to Euclid’s Geometry Chapter 13-Surface Areas and Volumes
Chapter 6-Lines and Angles Chapter 14-Statistics
Chapter 7-Triangles Chapter 15-Probability
Chapter 8- Quadrilateral

NCERT Solutions for class 9 science 

Chapter 1-Matter in our surroundings Chapter 9- Force and laws of motion
Chapter 2-Is matter around us pure? Chapter 10- Gravitation
Chapter3- Atoms and Molecules Chapter 11- Work and Energy
Chapter 4-Structure of the Atom Chapter 12- Sound
Chapter 5-Fundamental unit of life Chapter 13-Why do we fall ill ?
Chapter 6- Tissues Chapter 14- Natural Resources
Chapter 7- Diversity in living organism Chapter 15-Improvement in food resources
Chapter 8- Motion Last years question papers & sample papers

NCERT Solutions for class 10 maths

Chapter 1-Real number Chapter 9-Some application of Trigonometry
Chapter 2-Polynomial Chapter 10-Circles
Chapter 3-Linear equations Chapter 11- Construction
Chapter 4- Quadratic equations Chapter 12-Area related to circle
Chapter 5-Arithmetic Progression Chapter 13-Surface areas and Volume
Chapter 6-Triangle Chapter 14-Statistics
Chapter 7- Co-ordinate geometry Chapter 15-Probability
Chapter 8-Trigonometry

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Chapter 1- Chemical reactions and equations Chapter 9- Heredity and Evolution
Chapter 2- Acid, Base and Salt Chapter 10- Light reflection and refraction
Chapter 3- Metals and Non-Metals Chapter 11- Human eye and colorful world
Chapter 4- Carbon and its Compounds Chapter 12- Electricity
Chapter 5-Periodic classification of elements Chapter 13-Magnetic effect of electric current
Chapter 6- Life Process Chapter 14-Sources of Energy
Chapter 7-Control and Coordination Chapter 15-Environment
Chapter 8- How do organisms reproduce? Chapter 16-Management of Natural Resources

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Chapter 1-Sets Chapter 9-Sequences and Series
Chapter 2- Relations and functions Chapter 10- Straight Lines
Chapter 3- Trigonometry Chapter 11-Conic Sections
Chapter 4-Principle of mathematical induction Chapter 12-Introduction to three Dimensional Geometry
Chapter 5-Complex numbers Chapter 13- Limits and Derivatives
Chapter 6- Linear Inequalities Chapter 14-Mathematical Reasoning
Chapter 7- Permutations and Combinations Chapter 15- Statistics
Chapter 8- Binomial Theorem  Chapter 16- Probability

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Chapter 1-Relations and Functions Chapter 9-Differential Equations
Chapter 2-Inverse Trigonometric Functions Chapter 10-Vector Algebra
Chapter 3-Matrices Chapter 11 – Three Dimensional Geometry
Chapter 4-Determinants Chapter 12-Linear Programming
Chapter 5- Continuity and Differentiability Chapter 13-Probability
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Chapter 8-Application of Integrals

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