Asubstance that contains only one kind of matter is known as a(n)
a. atom.
b. element.
c. molecule.
d. compound.

B. element.

Explanation:

An atom is the smallest unit of any matter which may or may not have independent existence.

Element is a pure substance which is composed of atoms of similar elements.It can not be decomposed into simpler constituents using chemical reactions.Example: Copper

Molecule is the smallest unit of any matter which always have independent existence.

Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.It can be decomposed into simpler constituents using chemical reactions. Example: water

1. a)c-14 has two more protons

2. d)they have different numbers of protons, neutrons, and valence electrons; they are all gases at room temperature.

3. c) iron and nickel.

what are the statements