CBSE Class 9 Science Exam 2020-21: NCERT Based Important Extra Questions (With Answers) Chapter 3 - Atoms & Molecules

CBSE: Check important extra questions for the upcoming CBSE Class 9 Science exam 2020-21 from Chapter 3 (Atoms & Molecules) of Class 9 Science NCERT textbook. Answers of all the questions are also available here. Time duration to attempt these questions in 5 minutes. Students with sound knowledge of basic concepts of this chapter can easily attempt these questions in one go. These questions might be also asked in CBSE School examinations with slight modification. 

CBSE Class 9 Science Exam 2020-21: NCERT Based Important Extra Questions With Answers Chapter 3 - Atoms & Molecules

Question: How many atoms are there in the 18 g of water? 

Answer: 3NA [NA is Avogadro number and its value is 6.02×1023]

The Number of atoms = [(mass of substance)/(molar mass) x NA x (Number of atoms in the molecule)]

The Number of atoms = [(18)/(18) x NA x (3)] = 3 NA 

[NA is Avogadro number and its value is 6.02×1023]

NCERT Solutions for Class 9 - Maths, Science, Social Science and English (Chapter-Wise PDF)

Question: 360 g of water can also be written as 20 moles of water. Explain.

Answer:

1 mole of water = 18 g (18 g is molar mass of water)

So, 18 moles of water = 360 g 

20 moles of water = 20 ×18 g = 360 g.

Question:

Calculate the number of moles of magnesium present in a magnesium ribbon weighing 48 g.

Answer: 2 mole.

Molar atomic mass of magnesium is 24 g mol–1.

Moles of magnesium = (total mass)/(molar atomic mass) = 48/24 = 2 moles.

Question: Fill in the blanks

Inert gases exist in ________.

(a) tetratomic form

(b) triatomic form

(c) diatomic form

(d) monoatomic form

Answer: (d)

Inert gases exist in monoatomic form.

Question: Find the number of atoms present in each of the following chemical species CO32–.

Answer:

4 atoms.

CBSE Class 9 Science Chapter Notes