Atoms and Molecules Quiz - CBSE Class 9 Science
Free practice quiz: Atoms and Molecules (CBSE Class 9 Science). 16 multiple-choice questions with answers and explanations. Play online, no sign-up needed.
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What is an atom?
- A pure substance made of two or more elements
- The smallest unit of matter
- A type of molecule
- A chemical reaction
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Answer: B. The smallest unit of matter
An atom is the smallest unit of matter that retains the properties of an element.
Which of the following correctly represents a compound?
- NaCl
- He
- O2
- N
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Answer: A. NaCl
NaCl (sodium chloride) is a compound formed from the combination of sodium and chlorine atoms.
Which of the following statements is true about atoms and elements?
- All atoms are identical
- An element consists of only one type of atom
- Atoms can be created or destroyed in a chemical reaction
- Elements can exist as molecules
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Answer: B. An element consists of only one type of atom
An element is defined as a pure substance that cannot be broken down into simpler substances and consists of only one type of atom.
Which law states that mass is neither created nor destroyed in a chemical reaction?
- Law of Conservation of Mass
- Law of Definite Proportions
- Law of Multiple Proportions
- Law of Chemical Equilibrium
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Answer: A. Law of Conservation of Mass
The Law of Conservation of Mass states that the total mass of reactants is equal to the total mass of products in a chemical reaction.
Which of the following describes how chemical formulas represent compounds?
- They show the number of protons
- They indicate the ratio of different elements
- They represent only the physical state
- They show the mass of elements
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Answer: B. They indicate the ratio of different elements
Chemical formulas represent compounds by indicating the types and ratio of atoms (elements) that make up the compound.