# Which substance is an element? Which is a liquid? An element? Which substance is made of ions?

As far as we know $\text{B is a liquid.}$ $\text{D is an ion}$. $\text{C}$ is probably a gas (e.g. $C {O}_{2}$). Presumably, $\text{A}$ contains only the one type of particle, i.e. the one type of atom, and could thus be classified as an element.