1what is a material that contains three elements joined in a fixed proportion?
a mixture
b solution
c atom
d compound

d Compound is a thing made up to two or more separate elements joined in a proper proportion

Mixture cannot be the correct answer because mixture can be made up of multiple substances i.e it can be more than three also.

Solution cannot be the correct answer because solution is made up of only  solute and solvent.

Atom is the smallest unit made up of  smallest constituent unit and cannot be further differentiated

A material that contains three elements joined in a fixed proportion is .

Further explanation:

Pure substances:

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.

Solution:

A homogeneous mixture that is composed of two or more substances is called a solution. It has two components, solute, and solvent. The component present in smaller amount is called solute while that present in larger quantity is solvent.

Atom:

The smallest particle that is the building block of matter is known as an atom. Most of the space in an atom is empty and its mass is concentrated inside a small region called the nucleus.

(a) Mixture does not have any specific formula, and it has a variable composition. So it is an incorrect option.

(b) Solution is a homogeneous mixture that consists of two components, one is solute, and the other is solvent. So it is an incorrect option.

(c) Atom is the smallest entity that participates in any chemical reaction. It is composed of three subatomic particles. These are electrons, protons, and neutrons. So it is an incorrect option.

(d) Compound is a type of pure substance that is made by the chemical combination of elements in a fixed specific ratio. So it is a correct option.

Learn more:

1. Which sample is a pure substance? link

2. Which is a characteristic of a  mixture? link

Answer details:

Grade: High School

Subject: Chemistry

Chapter: Elements, compounds, and mixtures

Keywords: mixture, pure substance, elements, compounds, formula, composition, simplest form of substance, atom, solution, correct, incorrect.

explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.

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the must be sensory neurons.  

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