What are hydronium and hydroxide ions?

Hint: An ion is a molecule, iota or atom with a net electrical charge. A cation is a particle that is positively charged and it contains fewer electrons than protons while an anion is a particle which is negatively charged and it has a larger number of electrons than protons.

Complete step by step answer:
We should know that hydronium is the normal name for the aqueous cation $\left( {{H_3}{O^ + }} \right)$ , the kind of oxonium particle formed by protonation of water. It is the positive particle present when an Arrhenius acid is disintegrated in water, as molecules of Arrhenius acid in arrangement surrender a proton (a positive hydrogen particle, ${H^ + }$) to the encompassing molecules of water $\left( {{H_2}O} \right)$. We can write the symbol of hydronium ion is ${H_3}{O^ + }$.
We have to know that hydroxide is a diatomic anion with the chemical equation $O{H^ - }$ . It comprises an oxygen and hydrogen particle held together by a solitary covalent bond, and comprises negative electric charge. Hydroxide ion is a significant whereas slight entity of water. We have to know that hydroxide ion plays the role of base, nucleophile, ligand, and catalyst. A hydroxide connected to an emphatically electropositive focus may itself ionize, freeing a hydrogen cation ${H^ + }$, and this turns the parent compound into an acid.
We have to know that the hydroxide particle is a characteristic piece of water in view of the self-ionization reaction where its supplement, hydronium, is passed hydrogen:

Note: In simple words, we can say that hydronium ion is the cation of water and hydroxide ion is the anion of water. We can calculate the pH of an acidic solution using the concentration of hydronium ion and we can calculate the pOH of a basic solution using the concentration of hydroxide ion. We can multiply the concentration of hydroxide ion and concentration of hydronium ion to get an ionization constant of water $\left( {{K_w}} \right)$. We can write the expression of ionization constant for water as,
${K_w} = \left[ {{H_3}{O^ + }} \right]\left[ {O{H^ - }} \right]$