Substances can be pure or they can be mixture. Which of these is a mixture a) Oxygen b) Air C) Gold d) carbon dioxide
b) Air
The correct option for a mixture is b) Air.
Oxygen (a) can exist in a pure form as an element, but it can also be present as a component in a mixture.
Gold (c) is typically considered a pure substance as it is an element that exists in its elemental form.
Carbon dioxide (d) can exist as a pure substance or a mixture, depending on the context. In a closed system, it can exist as a pure substance. However, in the atmosphere, it is present as a component of air, making it a mixture.
To determine whether a substance is a mixture or pure, we need to understand the definitions of both.
A pure substance is composed of only one type of atom, molecule, or compound. It cannot be broken down into simpler parts by physical or chemical means. On the other hand, a mixture is a combination of two or more pure substances that are physically combined and can be separated using physical methods.
Now, let's analyze the given options:
a) Oxygen: Oxygen can exist in different forms, such as O2 (diatomic), O3 (ozone), or O (monatomic). Regardless of its form, oxygen is a pure substance because each form contains only oxygen atoms. Therefore, it is not a mixture.
b) Air: Air is a mixture composed of several gases, predominantly nitrogen (about 78%), oxygen (about 21%), carbon dioxide, argon, and traces of other gases. Since air is a combination of different gases, it is considered a mixture.
c) Gold: Gold, in its pure form, is a chemical element with the symbol Au (from the Latin word for gold, "aurum"). Gold does not consist of different substances but is composed solely of gold atoms, so it is a pure substance.
d) Carbon dioxide: Carbon dioxide (CO2) is a compound made up of carbon and oxygen atoms. It is considered a pure substance because it is a specific compound with a fixed ratio of carbon to oxygen atoms.
Based on this analysis, the mixture among the given options is b) Air.