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

the answer is 1260

you spend 7 hours in school for 1 school day with 5 school days in 1 school week with 36 school weeks in a school year.

7*5*36= 1260 it's all about multiplying

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)