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9th CBSE
IMPORTANT
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An atom of magnesium weighs 3.98×10-23 g. The number of atoms present in 12 g of magnesium is:

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Important Questions on Atoms and Molecules

EASY
9th CBSE
IMPORTANT
Core science chemistry>Chapter 3 - Atoms and Molecules>EXERCISE 3A>Q 1
State the law of conservation of mass.
EASY
9th CBSE
IMPORTANT
Core science chemistry>Chapter 3 - Atoms and Molecules>EXERCISE 3A>Q 2
State the law of definite proportions.
MEDIUM
9th CBSE
IMPORTANT
Core science chemistry>Chapter 3 - Atoms and Molecules>EXERCISE 3A>Q 1
In a reaction, 10 g of calcium carbonate reacts with 7.3 g of hydrochloric acid. The products of reaction are 11.1 g of calcium chloride, 1.8 g of water and 4.4 g of carbon dioxide gas. Show that these observations are in agreement with the law of conservation of mass.
MEDIUM
9th CBSE
IMPORTANT
Core science chemistry>Chapter 3 - Atoms and Molecules>EXERCISE 3A>Q 2
Magnesium and oxygen combine in the ratio of 3:2 by mass to form magnesium oxide. How much mass of oxygen is required to react completely with 12 g of magnesium?
MEDIUM
9th CBSE
IMPORTANT
Core science chemistry>Chapter 3 - Atoms and Molecules>EXERCISE 3A>Q 3
Which postulate of Dalton's atomic theory can explain: 
(a) the law of conservation of mass, 
(b) the law of definite proportion?
MEDIUM
9th CBSE
IMPORTANT
Core science chemistry>Chapter 3 - Atoms and Molecules>EXERCISE 3A>Q 4
Name one Indian and one foreign ancient thinker, who proposed the atomic nature of matter.
EASY
9th CBSE
IMPORTANT
Core science chemistry>Chapter 3 - Atoms and Molecules>EXERCISE 3A>Q 5
Name 
(a) an element, 
(b) an isotope of the element, used as atomic mass unit.
MEDIUM
9th CBSE
IMPORTANT
Core science chemistry>Chapter 3 - Atoms and Molecules>EXERCISE 3A>Q 6
In an experiment, 9.6 g of sulphur bums completely in 9.6 g of oxygen to produce 19.2 g of sulphur dioxide. In another experiment, 9.6 g of sulphur is made to bum completely in 100 g of oxygen. What mass of sulphur dioxide is formed. Which law of chemical combination governs your answer?