Which of the answer choices best describes elements?
a. homogenous mixtures
b. always solid
c. very dense
d. pure substances

It can be a compound or a single element. An element is a pure substance that cannot be separated into simpler substances by chemical or physical means. There are about 117 elements, butcarbon, hydrogen, nitrogen and oxygen are only a few that make up the largest portion of Earth.

I would say d.

Anions are negative charged ions