NCERT Solutions for Class 9 Science Chapter 3: Atoms and Molecules

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The NCERT Solutions for Class 9 Science are provided in this article. Some of the important topics in Chapter 3 Atoms and Molecules include:

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NCERT Solutions for Class 9 Science Chapter 3

NCERT Solutions

NCERT Solution

Class 9 Science Chapter 3 Atoms and Molecules – Important Topics

Atom is the smallest constituent unit of matter that possess the properties of the chemical element. Atoms don’t exist independently, instead, they form ions and molecules which further combine in large numbers to form matter that we see, feel and touch.

Dalton’s Atomic Theory

Dalton’s Atomic Theory hypothesized and further claimed that the law of conservation of mass and the law of definite proportions could possibly de elaborated by using the idea of atoms. According to him, all substances are indestructible building units.

Example: What are two postulates of Dalton’s Atomic Theory?

Solution: The two postulates of Dalton’s Atomic Theory are:

The substances around us are composed of matter, which are tiny, indestructible particles called atoms.
Every atom of a particular element are identical according to their mass, size, and several other properties.

Atomic Mass

The complete mass of one atom of a distinct element can be otherwise called as its atomic mass. The unit it has is known as unified atomic mass unit, that is represented by the letter ‘u.’

Example: Calculate the atomic mass of an oxygen isotope that has 9 neutrons.

Solution: To calculate the atomic mass of an oxygen isotope, we need to know the number of protons and neutrons it has.
Number of protons in an oxygen atom = 8
As per the question, the Number of neutrons in oxygen atom = 9
Hence, the Atomic mass of given oxygen atom = number of protons + number of neutrons = 8 + 9 = 17

Mole Concept

Mole concept can be defined as the atomic mass of a mole which is usually measured in grams. Ideally, the gram atomic mass of an element is otherwise referred to as a mole.

Example: What is the formula of Mole Concept?

Solution: The number of units responsible to compose mole can be evaluated by 6.022 ×10²³. The fundamental constant is called the Avogadro's number (NA) or Avogadro constant. It can be represented using an explicit unit termed per mole. Thus, to calculate Mole Concept,
Number of Moles = (Mass of the Sample)/(Molar Mass)

Read Also:

Chapter Related Links
Avogadro's Law	Difference between Molar Mass and Molecular Mass	Atomic Mass Formula
Moles to Grams Formula	Number of Moles Formula	Nucleus of an Atom and Atomic Mass
Atomic Number	Atomic And Molecular Masses	Mole Fraction

Also Check:

Important Science Study Guides
Physics Constants	Named Reactions	Difference between in chemistry
Difference between in biology	Difference between in physics	Periodic Table

CBSE X Related Questions

1.
Plants use variety of techniques to get rid of their waste materials. Some are mentioned below. Identify the incorrect one:
- Excess water is given out by transpiration.
- Gums and Resins are wastes that are stored.
- Roots secrete some wastes into the soil.
- Flowers can store some waste products.
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2.
Given below is a pyramid showing various trophic levels in an ecosystem:
(a) From the organisms listed below, identify which one is to be placed at which trophic level:
Deer, Grass, Lion, Snake, Rabbit
(b) Discuss the reason why primary consumers will have more energy as compared to secondary consumers?
(c) Why is the base of the pyramid broad?
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3.
Briefly mention the steps in double-circulation through human heart.
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4.
From the given situations, identify 'Chemotropic' and 'Geotropic' movements in parts of plants, respectively:
(i) Growth of pollen tube towards ovule.
(ii) Movement of sunflower towards sunlight.
(iii) Movement of root towards Earth/Gravity.
(iv) Movement of leaves due to breeze.
- (i) and (iii) respectively
- (iii) and (i) respectively
- (i), (ii) and (iii), (iv) respectively
- (i), (iii) and (ii), (iv) respectively
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5.
Identify the correct statement for spirogyra, leishmania and hydra
- they reproduce sexually.
- they are unicellular.
- they are multicellular.
- they reproduce asexually.
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6.
Assertion (A): Reflex actions do not involve thinking.
Reason (R): Most reflex actions are controlled by the spinal cord.
- Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
- Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
- Assertion (A) is true, but Reason (R) is false.
- Assertion (A) is false, but Reason (R) is true.
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