Which best describes an element? a. a pure substance b. a type of mixture c. a pure compound d. an impure substance

a. Pure substance

Explanation:

We have to choose which describes best an element.

Pure substance : It is defined as an element which can not be split into smaller particles by chemical or physical method.

Mixture: It is that particles which consist of same type atoms or two or more than two type of an atom with definite and constant composition .

Pure compound : It is also consist of two or more than two type of atoms or molecules such as methane gas.

An impure substance: It that substance which consist of atoms and some type  of impurities .

An element is a pure substance which  can not be broken into smallest particle by chemical reaction.

Option a best describes an element

Option (a) is the correct answer.

Explanation:

An element is defined as a substance which contains same type of atoms. An element is a pure substance as there are same type of atoms and it cannot be broken down into its constituent particles.

For example, a piece of sodium metal is an element.

A mixture is a substance which contains two or more number of substances that are not chemically combined together.

A pure compound is a substance which contains two elements which are chemically combined together in a fixed ratio by mass.

Thus, we can conclude that a pure substance best describes an element.

the potential energy of the reactants is 200j.

from the energy diagram, the energy of the product formed is 350j; this means that, this reaction is an endothermic reaction, because it absorbs energy from its environment.

acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.