When H forms a bond with H2O to form the hydronium ion H3O , this bond is called a coordinate covalent bond because

both bonding electrons come from the oxygen atom

Explanation:

A coordinate covalent bond is said to be formed when an electron pair is donated into a empty orbital of an atom from a filled orbital of another atom.

In this type of covalent bond, the shared electron pair is furnished by only one of the bonding species.

The bonding between H^+ and H2O to form H3O^+ involves donation of a lone pair of electrons on oxygen into the empty 1s orbital of  H^+ hence the two bonding electrons come from oxygen. This is why the bond is called a coordinate covalent bond.

because u need two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei to form isotopes.

so since they all have the same shape? i mean maybe because m& m and reeses are both chocolates