The sample that is a pure substance is boxed{{text{(A) a test tube of zinc oxide}};}

Further Explanation:

Pure substance:

The substances that are made up of only one kind of atoms or molecules are known as pure substances. It is generally called as a chemical substance. Any substance is also said to be pure if it has a constant composition. Water, tin, diamond, sulfur, sodium chloride are some of the examples of pure substances.

Pure substances are of two types:

1. Elements:

An element is the simplest form of substance that cannot be broken down by any chemical methods. Every element has its own characteristic atomic number that is used to distinguish it from other elements. Copper, iron, neon, cobalt are examples of elements.

2. Compounds:

These are the substances formed by the chemical combination of two or more elements in a specific ratio. If the same elements are mixed in any other ratio, different compounds will be formed. These can be further broken down into their constituent elements.

Mixture:

The material that is made up of two or more substances is called a mixture. It has no fixed formula and its composition is also varied. All the individual constituents retain their properties after the formation of the mixture. Air, blood, concrete, and soda are some examples of mixtures.

(A) Zinc oxide is a compound that consists of zinc and oxygen atoms in the ratio 1:1 so it is a pure substance.

(B) Zinc and oxygen are present in the same container but are not chemically bonded to each other so it is not a pure substance.

(C) Pond water is a mixture of water and other impurities like soil, pebbles, bacteria. So it is not a pure substance.

(D) Soil is considered as a mixture of clay, sand and some organic substances like water and dead plant remains. So it is not a pure substance.

Learn more:

1. Identification of ionic bonding: brainly.com/question/1603987

2. Example of physical change: brainly.com/question/1119909

Answer details:

Grade: High School

Subject: Chemistry

Chapter: Elements, compounds and mixtures

Keywords: mixture, pure substance, soil, pond water, zinc, oxygen, zinc oxide, formula, substances, composition, individual, constituents.