Chapter 3.  Atoms and Molecules 

Class 9 Science Examplar Chapter 3 :  ATOMS AND MOLECULES Choose the correct answers :

Q1. The Avogadro constant is :

(A)  

(B)  

(C)  

(D)   

Q2. The formula unit mass of   is :

(A) 112u

(B) 123u

(C) 111u

(D) 110u

Ans : (C) 111u

Q3. The molecular mass of   is :

(A) 63u

(B) 61u

(C) 62u

(D) 64u

Q4. Which of the following is the formula of Aluminium Chloride ?

(A)  

(B)  

(C)  

(D)   

Ans : (D)   

Q5. How many atoms are present in a   ion ?

(A) 3 atoms

(B) 4 atoms

(C) 5 atoms

(D) 7 atoms

Ans : (C) 5 atoms .

Q6. Which of the following are not polyatomic ions ?

(A)    

(B)    

(C)   

(D)    

Ans : (C)  

Q7. What is the mass of 1 mole of nitrogen atoms ?

(A) 28g

(B) 14g

(C) 16g

(D) 18g

Ans : (B) 14g

Q8. The atomicity of   is :

(A) 13

(B) 14

(C) 15

(D) 8

Ans : (B) 14

Q9. The valency of  Phosphate [  ] is :

(A) 2

(B) 3

(C) 1

(D) 4

Ans : (B) 3

Q10. Nitrogen molecules are :

(A) Mono-atomic

(B) Diatomic

(C) Tetra- atomic

(D) Poly-atomic

Ans : (B) Diatomic

Q11. The formula of quick lime is :

(A)   

(B)  

(C)   

(D)   

Ans : (A)

Q12. Which of the following correctly represents 360g of water ?

(i) 2 mole of  .

(ii) 20 moles of water .

(iii)   molecules of water .

(iv)   molecules of water .

(A) (i) only .

(B) (i) and (iv)

(C) (ii) and (iii)

(D) (ii) and (iv)

Ans : (D) (ii) and (iv)

Q13. Which of the following statements is not true about an atom ?

(A) Atoms are not able to exist independently .

(B) Atoms are the basic units from which molecules and ions are formed .

(C) Atoms are always neutral in nature .

(D) Atoms aggregate in large numbers to form the matter that we can see, feel or touch .

Ans : (A) Atoms are not able to exist independently .

Q14. The chemical symbol for nitrogen gas is :

(A) Ni                    (B)      

(C)                 (D) N

Ans : (B)       

Q15. The chemical symbol for sodium is :

(A) So         (B) Sd            (C)  NA      (D) Na

Ans :  (D) Na        

Q16. Which of the following would weigh the highest ?

(A) 0.2 mole of sucrose ( )

(B) 2 moles of   

(C) 2 moles of 

(D) 10 moles of 

Ans :  (C) 2 moles of   .

Q17. Which of the following has maximum number of atoms ?

(A) 18g of                                           

(B) 18g of  

(C) 18g of   

(D) 18g of   

Ans :  (D) 18g of   

Q18. Which of the following contains maximum number of molecules ?

(A) 1g   

(B) 1g  

(C) 1g   

(D) 1g  

Ans :  (C) 1g   

Q19. Mass of one atom of oxygen is :

(A)     g

(B)    g

(C)    g

(D) 8u

Ans :  (A)   g

Q20. 3.42g of sucrose are dissolved in 18g  of water in a beaker . The number of oxygen atoms in the solution are :

(A) 

(B)   

(C) 

(D) 

Ans :  (A) 

Q21. A change in the physical state can be brought about

(A) only when energy is given to the system .

(B) only when energy is taken out  from the system

(C) when energy is either given to , or taken out from the system

(D) without any energy change

Ans :  (C) when energy is either given to ,or taken out from the system .

Q22. Which of the following statement is not correct ?

(A) All matter is made of very tiny particles called atoms .

(B) Atoms of different elements have different masses and chemical properties .

(C)  Atoms are indivisible particles, which can be created or destroyed in a chemical reaction .

(D) Atoms of a given element are identical in mass and chemical properties .

Ans : (C)  Atoms are indivisible particles, which can be created or destroyed in a chemical reaction .

[ Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction .]  

Q23. How many moles are 28 g of Nitrogen atoms :

(A) 1 mole

(B) 1.5 mole

(C) 0.5 mole

(D) 2 mole

Ans : (D) 2 mole .

Q24. All noble gas molecules are :

(A) Mono-atomic

(B) di-atomic

(C) tri-atomic

(D) both (A) and (B)

Ans :  (A) Mono-atomic .

Q25. The latin name of Gold is :

(A) Aurum

(B) Natrium

(C) Kalium

(D) Hydrargyrum .

Ans :   (A) Aurum .

Q26. The molecular mass of   is :

(A)  18u

(B) 16u

(C) 20u

(D) 36u

Ans : (A)  18u

Class 9 Science Examplar Chapter 3 : ATOMS AND MOLECULES Fill in the blanks :

Q27. In a chemical reaction , the sum of the masses of the reactants and products remains unchanged . This is called  .

Ans : Law of conservation of mass .

Q28. A group of atoms carrying a fixed charge on them is called  .

Ans : Polyatomic ion .

Q29. The formula unit mass of      is  .

Ans : 310 u

Q30. Formula of sodium carbonate is and that of ammonium sulphate is  .

Ans :    ,    .