To define a 'pure substance', we need to recall its fundamental characteristics in chemistry. A pure substance is distinct from a mixture and has specific, unchanging properties.
Correct Option: B) A substance that consists of a single type of particles, all having the same chemical nature, with a fixed composition and definite properties
To identify pure substances, we need to understand their definition. A pure substance is a form of matter that has a constant chemical composition and characteristic properties. It cannot be separated into simpler substances by physical means. Pure substances are either elements (composed of only one type of atom) or compounds (composed of two or more elements chemically combined in a fixed ratio).
Correct Option: D) Gold, silver, water, common salt (sodium chloride), oxygen
The question asks for the definition of a 'mixture' according to NCERT Class 9 Chapter 2. We need to evaluate each option against the standard definition of a mixture and distinguish it from pure substances (elements and compounds).
Correct Option: D) A substance formed when two or more substances are combined in any ratio and each substance retains its own chemical identity.
The question asks to identify the statement that correctly differentiates between a compound and a mixture. To answer this, we need to recall the fundamental definitions and characteristics of compounds and mixtures in chemistry.
B) In a compound, elements are chemically combined in a fixed ratio; in a mixture, substances are physically combined in any ratio. This statement correctly highlights the fundamental differences in chemical bonding and composition ratios between compounds and mixtures.
To classify air correctly, we need to understand the definitions of different types of substances: elements, compounds, homogeneous mixtures, and heterogeneous mixtures. We will then analyze the composition and properties of air based on these definitions.
C) A homogeneous mixture — Air is a mixture of several gases (like nitrogen, oxygen, argon, carbon dioxide) that are uniformly distributed throughout, and their individual components cannot be seen separately. They are not chemically bonded, and their proportions can vary slightly, which is characteristic of a mixture, not a pure substance (element or compound).
The question asks to classify an alloy based on NCERT Class 9 chemistry concepts. We need to recall the definitions of mixtures, pure substances, elements, and compounds, and how alloys fit into these classifications.
A) A mixture — because alloys can have variable composition and their components retain their individual properties. This statement accurately describes an alloy according to the definition of a mixture and aligns with NCERT Class 9 classification. Alloys are homogeneous mixtures where the constituents are not chemically bonded and their proportions can vary.