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Atoms and Molecules CBSE Class 9

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Atoms and Molecules Topics

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Question 1/20

Q 1. What is the relative atomic mass of oxygen? 

Solution

The relative atomic mass of oxygen is 16. 

Q 2. Which of the following is not a law of chemical combination? 

Solution

Law of infinite proportions is not a law of chemical combination. 

Q 3. Which of the following is a symbolic representation of its composition of a compound? 

Solution

Chemical formula is a symbolic representation of the composition of a compound. 

Q 4. How many atoms of hydrogen are present in the hydrogen molecule? 

Solution

Two atoms of hydrogen combine to form the hydrogen atom. 

Q 5. Which among these was a first person to recognize a workable distinction between the fundamental particle of an element and compound? 

Solution

John Dalton was a first person to recognize a workable distinction between the fundamental particle of an element and compound 

Q 6. Chemical equations are balanced according to the law of 

Solution

Chemical equations are balanced according to the law ofconservation of mass. 

Q 7. The number of atoms present in potassium dichromate K2Cr2O7 is 

Solution

The number of atoms present in potassium dichromate K2Cr2O7 is 11. 

Q 8. Sulphur forms two oxides SO2 and SO3 in accordance with 

Solution

Sulphur forms two oxides SO2 and SO3 in accordance withlaw of multiple proportional. 

Q 9. Which of the following is not a postulate of Dalton’s theory? 

Solution

Dalton's atomic theory states that, matter is made of indivisible particles called atoms which can neither be created nor destroyed. 

Q 10. What is the black compound formed on silverware? 

Solution

The black compound formed on silverware is silver sulphide. 

Q 11. A chemical compound always contains exactly the same proportion of elements by mass. Which among the following statements is related? 

Solution

Law of definite proportions states that a chemical compound always contains exactly the same proportion of elements by mass. 

Q 12. The average mass of the isotopes of the element as compared to 1/12 the mass of one carbon-12 atom is known as 

Solution

The relative atomic mass is the average mass of the isotopes of the element as compared to 1/12 the mass of one carbon-12 atom. 

Q 13. Which of the following does not exist as a molecule? 

Solution

Helium does not exist as a molecule; it is a monatomic gas. 

Q 14. If the valency of X is 1, then what will be the chemical formula of the nitride? 

Solution

If the valency of X is 1, then the chemical formula of the nitride is XN3. 

Q 15. Carbon reacts with oxygen forms CO and CO2 in the ratio of 12:16 and 12:32. These figures show 

Solution

Carbon reacts with oxygen forms CO and CO2 in the ratio of 12:16 and 12:32. These figures show law of multiple proportional. 

Q 16. Two molecules of oxygen are represented by 

Solution

Two molecules of oxygen are represented by 2O2. 

Q 17. Who named the indivisible particle of matter as an atom? 

Solution

Democritus named the indivisible particle of matter as an atom. 

Q 18. Find the major drawback of Dalton’s theory 

Solution

the major drawback of Dalton’s theory is atoms are indivisible. Atom is further divided into protons, neutrons and electrons. 

Q 19. An atom is 16 times heavier than 1/12th of the mass of the carbon atom (C-12 isotope). The mass in a.m.u. is 

Solution

An atom is 16 times heavier than 1/12th of the mass of the carbon atom (C-12 isotope). The mass in a.m.u. is 16. 

Q 20. Which of the following elements is a monatomicmonoatomic gas? 

Solution

Ne is a monoatomic gas. 

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