Which of the following statements about elements and compounds is/are correct? 1. Some elements exist as diatomic molecules under ordinary conditions. 2. The properties of a compound are identical to those of its constituent elements. 3. An element consists of only one type of atom. Select the correct answer using the code given below.

Correct Option The correct option is 1 and 3 only. Explanation Matter is classified into elements, compounds, and mixtures based on chemical composition. An element is a pure substance consisting of only one type of atom, whereas a compound is formed when two or more elements combine chemically in a fixed ratio. Statement-wise Analysis - Statement 1 is Correct: While many elements exist as single atoms (monoatomic), several non-metallic elements exist as diatomic molecules under ordinary conditions to achieve stability. Examples include Hydrogen ($H_2$), Nitrogen ($N_2$), and Oxygen ($O_2$). - Statement 2 is Incorrect: When elements combine to form a compound, they lose their individual properties, and the resulting compound acquires entirely new chemical and physical properties. For example, Sodium ($Na$) is a reactive metal and Chlorine ($Cl$) is a toxic gas, but they combine to form Sodium Chloride ($NaCl$), which is common table salt. Similarly, water ($H_2O$) extinguishes fire, whereas its constituents, Hydrogen and Oxygen, are combustible and supporters of combustion, respectively. - Statement 3 is Correct: By definition, an element is a pure substance composed of identical atoms that have the same atomic number (number of protons). It cannot be broken down into simpler substances by ordinary chemical means. Key Takeaway Key Takeaway: Elements consist of a single type of atom and may exist as monoatomic or polyatomic molecules (e.g., $O_2$, $P_4$). Compounds are chemically bonded combinations of different elements with properties distinct from their constituents.

NCERT Class 11 Science — Chapter 1: Some Basic Concepts of Chemistry

mcqmedium

Which of the following statements about elements and compounds is/are correct?

Some elements exist as diatomic molecules under ordinary conditions.
The properties of a compound are identical to those of its constituent elements.
An element consists of only one type of atom.

Select the correct answer using the code given below.

Official previous-year question

Verified 1 Aug 2026.

Options

A1 and 3 only
B2 only
C1 and 2 only
D1, 2 and 3

Did you get this right?

Solution

Correct Option

The correct option is 1 and 3 only.

Explanation

Matter is classified into elements, compounds, and mixtures based on chemical composition. An element is a pure substance consisting of only one type of atom, whereas a compound is formed when two or more elements combine chemically in a fixed ratio.

Statement-wise Analysis

Statement 1 is Correct: While many elements exist as single atoms (monoatomic), several non-metallic elements exist as diatomic molecules under ordinary conditions to achieve stability. Examples include Hydrogen ($H_2$), Nitrogen ($N_2$), and Oxygen ($O_2$).
Statement 2 is Incorrect: When elements combine to form a compound, they lose their individual properties, and the resulting compound acquires entirely new chemical and physical properties. For example, Sodium ($Na$) is a reactive metal and Chlorine ($Cl$) is a toxic gas, but they combine to form Sodium Chloride ($NaCl$), which is common table salt. Similarly, water ($H_2O$) extinguishes fire, whereas its constituents, Hydrogen and Oxygen, are combustible and supporters of combustion, respectively.
Statement 3 is Correct: By definition, an element is a pure substance composed of identical atoms that have the same atomic number (number of protons). It cannot be broken down into simpler substances by ordinary chemical means.

Key Takeaway

Key Takeaway: Elements consist of a single type of atom and may exist as monoatomic or polyatomic molecules (e.g., $O_2$, $P_4$). Compounds are chemically bonded combinations of different elements with properties distinct from their constituents.

Your note

More from Chapter 1: Some Basic Concepts of Chemistry

What is the correct symbol for the SI unit ‘mole’?

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Who is credited with proposing the Law of Conservation of Mass?

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Which of the following are considered chemical properties of matter? 1. Melting point 2. Boiling point 3. Acidity 4. Reactivity with acids Select the correct answer using the code given below.

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Which international body and treaty are responsible for the maintenance of the SI unit system?

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Who is credited with proposing the Law of Definite Proportions?

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Keep practising Chapter 1: Some Basic Concepts of Chemistry

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Solution

Correct Option

The correct option is 1 and 3 only.

Explanation

Statement-wise Analysis

Statement 1 is Correct: While many elements exist as single atoms (monoatomic), several non-metallic elements exist as diatomic molecules under ordinary conditions to achieve stability. Examples include Hydrogen ($H_2$), Nitrogen ($N_2$), and Oxygen ($O_2$).
Statement 2 is Incorrect: When elements combine to form a compound, they lose their individual properties, and the resulting compound acquires entirely new chemical and physical properties. For example, Sodium ($Na$) is a reactive metal and Chlorine ($Cl$) is a toxic gas, but they combine to form Sodium Chloride ($NaCl$), which is common table salt. Similarly, water ($H_2O$) extinguishes fire, whereas its constituents, Hydrogen and Oxygen, are combustible and supporters of combustion, respectively.
Statement 3 is Correct: By definition, an element is a pure substance composed of identical atoms that have the same atomic number (number of protons). It cannot be broken down into simpler substances by ordinary chemical means.