NCERT Class 9 Science — Chapter 2: Is matter around us pure?

mcqeasy

From a chemical classification perspective, 'Brass' is considered a:

Official previous-year question

Verified 1 Aug 2026.

Options

AHeterogeneous mixture of Zinc and Copper
BChemical compound of Zinc and Copper
CPure element containing traces of Zinc
DHomogeneous mixture of Zinc and Copper

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Solution

Correct Option

The correct option is

Homogeneous mixture of Zinc and Copper

Explanation

Matter is broadly classified into pure substances (elements and compounds) and mixtures (homogeneous and heterogeneous). Alloys are metallic materials composed of two or more elements. While they possess metallic bonding, from a strict chemical classification perspective, most common alloys are considered mixtures rather than chemical compounds.

Option Analysis

Chemical compound of Zinc and Copper is Incorrect: A chemical compound consists of elements combined in a fixed, stoichiometric ratio (e.g., H₂O or NaCl) and has properties distinct from its constituents. Brass does not have a fixed chemical formula; the ratio of Copper to Zinc can vary (e.g., 60:40 or 70:30) to produce different types of brass. Therefore, it is not a chemical compound.
Homogeneous mixture of Zinc and Copper is Correct: Brass is an alloy formed by mixing molten Copper and Zinc, which then solidifies. It is classified as a homogeneous mixture (specifically, a solid solution) because the Zinc atoms are distributed uniformly within the Copper lattice. The composition is uniform throughout the bulk of the material, and the components cannot be separated by simple mechanical means, though they retain their individual chemical characteristics.
Heterogeneous mixture of Zinc and Copper is Incorrect: A heterogeneous mixture has a non-uniform composition where the components remain physically distinct (e.g., sand and iron filings). Brass appears uniform throughout and consists of a single phase, making it homogeneous rather than heterogeneous.
Pure element containing traces of Zinc is Incorrect: An element is a pure substance consisting of only one type of atom. Brass is composed of two distinct elements, Copper and Zinc.

Key Takeaway: Alloys are chemically classified as homogeneous mixtures (solid solutions) because they have a variable composition and their constituent elements are uniformly mixed at the atomic level without forming a fixed chemical compound.

Your note

More from Chapter 2: Is matter around us pure?

With reference to 'Alloys', consider the following statements: 1. They are considered mixtures because they show the properties of their constituents. 2. They can be separated into their components by physical methods. 3. They have a fixed composition and cannot vary. Which of the statements given above is/are correct?

medium

Consider the following statements regarding the properties of metals: 1. They are generally brittle and non-ductile. 2. They are generally good conductors of heat and electricity. 3. They are sonorous. Which of the statements given above is/are correct?

easy

Consider the following statements about elements: 1. The majority of elements are solids. 2. Only two elements are in the gaseous state at room temperature. 3. Gallium and Cesium remain solid even at temperatures well above 303 K. Which of the statements given above is/are correct?

medium

In the classification of colloids, 'Cheese' and 'Butter' are examples of:

medium

Consider the following statements regarding the burning of wood: 1. It involves the conversion of wood into new substances like ash and smoke. 2. It is a physical change. 3. It is an irreversible process. Which of the statements given above is/are correct?

easy

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Correct Option

The correct option is

Homogeneous mixture of Zinc and Copper

Explanation

Option Analysis

Chemical compound of Zinc and Copper is Incorrect: A chemical compound consists of elements combined in a fixed, stoichiometric ratio (e.g., H₂O or NaCl) and has properties distinct from its constituents. Brass does not have a fixed chemical formula; the ratio of Copper to Zinc can vary (e.g., 60:40 or 70:30) to produce different types of brass. Therefore, it is not a chemical compound.
Homogeneous mixture of Zinc and Copper is Correct: Brass is an alloy formed by mixing molten Copper and Zinc, which then solidifies. It is classified as a homogeneous mixture (specifically, a solid solution) because the Zinc atoms are distributed uniformly within the Copper lattice. The composition is uniform throughout the bulk of the material, and the components cannot be separated by simple mechanical means, though they retain their individual chemical characteristics.
Heterogeneous mixture of Zinc and Copper is Incorrect: A heterogeneous mixture has a non-uniform composition where the components remain physically distinct (e.g., sand and iron filings). Brass appears uniform throughout and consists of a single phase, making it homogeneous rather than heterogeneous.
Pure element containing traces of Zinc is Incorrect: An element is a pure substance consisting of only one type of atom. Brass is composed of two distinct elements, Copper and Zinc.