NCERT Solutions for Class 9 Science Chapter 3

NCERT Solutions for Class 9 Science Chapter 3 Atoms and Molecules download in PDF form updated for academic session 2020-21 in Hindi and English Medium based on new NCERT Books and following new CBSE Curriculum. 9th Science chapter 3 Page 32, Page 33, Page 35, Page 39, Page 40, Page 42 and Exercises answers with explanation in English Medium or पेज 36 के उत्तर, पेज 40 के उत्तर, पेज 44 के उत्तर, पेज 46 के उत्तर, पेज 48 के उत्तर and अभ्यास के प्रश्न उत्तर in Hindi Medium free to study online or in PDF form to use offline.

Download NCERT Solutions 2020-21 and NCERT Solutions Apps for other subjects are also in same format. All the contents are updated for new session based on latest CBSE Syllabus 2020-2021.

NCERT Solutions for Class 9 Science Chapter 3

Class:9
Subject:Science – विज्ञान
Chapter 3:Atoms and Molecules

9th Science Chapter 3 Answers in English & Hindi Medium

NCERT Solutions for Class 9 Science Chapter 3 Atoms and Molecules Exercise and Intext questions of all pages are given below to free download in PDF form. All the contents can be downloaded without any login or password. We have updated all the contents for new session 2020-21 for CBSE, UP Board, MP Board, etc., who are following NCERT Books 2020-21 and latest CBSE Syllabus 2020-21.

Why is a cation so named?

When electric current is passed through the solution of a salt like sodium chloride (NaCl), the positive ion (Na+) migrates towards cathode (negative electrode). It is therefore, called cation. Remember this:
(i) Positive ion migrating towards cathode on passing electric current is known as cation.
(ii) Negative ion migrating towards anode on passing electric current is known as anion.

The atomic mass of an element is in fraction. What does it means?

If the atomic mass of an element is in fraction, this means that it is existed in the form of isotopes. The atomic mass is the average atomic mass and it is generally fractional.

Why are chemical reaction according to law of conservation of mass?

In all chemical reactions, there is only exchange of reactants taking place when products are formed. Since there is no loss or gain of mass, the chemical reactions are according to law of conservation of mass.

Give one limitation of law of constant composition.

The law of constant composition does not hold when different isotopes of an element take part in the formation of a particular compound. For example,
In carbon dioxide (CO2)
By using C-12 isotopes, the ratio of C : O is 12 : 32.
By using C-14 isotopes, the ratio of C : O is 14 : 32.
This means that the two ratios are not the same.

Out of atoms and molecules which can exist independently?

Molecules can exist independently. However, the atoms of noble gases (He, Ne, Ar, Kr, Xe) can also exist independently.

Questions for Practice on 9th Science Chapter 3

Question 1
In what respect does Dalton’s Atomic theory hold good even today?
Answer 1:
atom has been found to be made up of sub-atomic particles like electrons, protons and neutrons. But it is still the smallest particle of matter which can take can take part in chemical combination.

Question 2:
Why is it necessary to balance a chemical equation?
Answer 2:
A chemical equation has to be balanced in order to satisfy the law of conservation of mass. According to the law, there is no change in mass when the reaction changes into the production. Therefore, the chemical equation has to be balanced.

Question 3:
What is basic different between atoms and molecules?
Answer 3:
Atoms except those of noble or inert gas elements cannot exist of their own. However, all molecules can have independent existence.

Important Questions on 9th Science Chapter 3

When 3.0 g of carbon is burnt in 8.00 g oxygen, 11.00 g of carbon dioxide is produced. What mass of carbon dioxide will be formed when 3.00 g of carbon is burnt in 50.00 g of oxygen? Which law of chemical combinations will govern your answer?
Carbon + Oxygen → Carbon dioxide
3g of carbon reacts with 8 g of oxygen to produce 11g of carbon dioxide. If 3g of carbon is burnt in 50g of oxygen, then 3g of carbon will react with 8 g of oxygen. The remaining 42 g of oxygen will be left un-reactive. In this case also, only 11g of carbon dioxide will be formed. The above answer is governed by the law of constant proportions.
हाइड्रोजन एवं ऑक्सीजन द्रव्यमान के अनुसार 1:8 के अनुपात में संयोग करके जल निर्मित करते हैं। 3 g हाइड्रोजन गैस के साथ पूर्ण रूप से संयोग करने के लिए कितने ऑक्सीजन गैस के द्रव्यमान की आवश्यकता होगी?
हाइड्रोजन : ऑक्सीजन = 1:8
1 g हाइड्रोजन की सम्पूर्ण अभिक्रिया के लिए जरुरी ऑक्सीजन = 8 g
इसलिए, 3 g हाइड्रोजन की सम्पूर्ण अभिक्रिया के लिए जरुरी ऑक्सीजन = 8×3 = 24 g
अतः, 3 g हाइड्रोजन गैस के साथ पूर्ण रूप से संयोग करने के लिए 24 g ऑक्सीजन गैस के द्रव्यमान की आवश्यकता होगी।
What is the mass of 4 mole of aluminium atoms (Atomic mass of aluminium = 27)?
The mass of 4 moles of aluminium atoms is (4 × 27)g = 108g
Convert into mole: 12g of oxygen gas.
32 g of oxygen gas = 1 mole
Then, 12g of oxygen gas = 12/32 mole = 0.375 mole
डाल्टन के परमाणु सिद्धांत का कौन-सा अभिगृहीत द्रव्यमान के संरक्षण के नियम का परिणाम है?
डाल्टन के परमाणु सिद्धांत का निम्नलिखित अभिगृहीत द्रव्यमान के संरक्षण के नियम का परिणाम है:
परमाणु अविभज्य सूक्ष्मतम कण होते हैं जो रासायनिक अभिक्रिया में न तो सृजित होते हैं न ही उनका विनाश होता है।
डाल्टन के परमाणु सिद्धांत का कौन-सा अभिगृहीत निश्चित अनुपात के नियम की व्याख्या करता है?
डाल्टन के परमाणु सिद्धांत का निम्नलिखित अभिगृहीत निश्चित अनुपात के नियम की व्याख्या करता है:
किसी भी यौगिक में परमाणुओं की सापेक्ष संख्या एवं प्रकार निश्चित होते हैं।
परमाणु द्रव्यमान इकाई को परिभाषित कीजिए।
परमाणु द्रव्यमान इकाई: कार्बन – 12 समस्थानिक के एक परमाणु द्रव्यमान के 1/12वें भाग को मानक परमाणु द्रव्यमान इकाई कहते हैं।
What is the mass of 0.2 mole of oxygen atoms?
Mass of one mole of oxygen atoms = 16g
Then, mass of 0.2 mole of oxygen atoms = 0.2 × 16g = 3.2g
एक परमाणु को आँखों द्वारा देखना क्यों संभव नहीं होता है?
परमाणु बहुत छोटे होते हैं। ये किसी भी छोटी वस्तु, जिसकी हम कल्पना या तुलना कर सकते हैं, से भी छोटे होते हैं। इसलिए एक परमाणु को आँखों द्वारा देखना संभव नहीं होता है।
जैसे: हाइड्रोजन के परमाणु की त्रिज्या 10^(-10) m होती है।
रासायनिक सूत्र का क्या तात्पर्य है?
किसी यौगिक का रासायनिक सूत्र उसके संघटक का प्रतीकात्मक निरूपण होता है। रासायनिक सूत्र किसी यौगिक के अणु में उपस्थित तत्वों को प्रतीकों के माध्यम से प्रकट करता है।
जैसे CaCO3 (कैल्सियम कॉर्बोनेट) में कैल्सियम का एक, कार्बन का एक तथा ऑक्सीजन के तीन परमाणु उपस्थित हैं।

CBSE NCERT Solutions for Class 9 Science Chapter 3 Atoms and Molecules page 32
CBSE NCERT Solutions for Class 9 Science Chapter 3 Atoms and Molecules intext questions page 33
NCERT Solutions for Class 9 Science Chapter 3 Page 35
CBSE NCERT Solutions for Class 9 Science Chapter 3 Atoms and Molecules intext questions page 39
CBSE NCERT Solutions for Class 9 Science Chapter 3 Atoms and Molecules intext questions page 39 in english medium
CBSE NCERT Solutions for Class 9 Science Chapter 3 Atoms and Molecules intext questions page 40
CBSE NCERT Solutions for Class 9 Science Chapter 3 Atoms and Molecules intext questions page 42
CBSE NCERT Solutions for Class 9 Science Chapter 3 Atoms and Molecules intext questions page 42
NCERT Solutions for Class 9 Science Chapter 3 Atoms and Molecules Exercises Question answers
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