In a dative (coordinate) bond, how are the electrons provided?

In a dative (or coordinate) bond, one atom indeed donates both electrons to the bond. This type of bond occurs when one atom has a lone pair of electrons and can share that pair with another atom that has an empty orbital, thus forming a covalent bond. The key characteristic of a dative bond is that the electron pair originates solely from one of the bonded atoms, making this arrangement distinct from a regular covalent bond where each atom typically contributes one electron.

To illustrate this concept further, consider the formation of ammonium ion (NH₄⁺), where the nitrogen atom donates its lone pair to bond with a hydrogen ion (H⁺). In this case, nitrogen is the donor of both electrons, leading to the formation of a coordinate bond.

Other options do not accurately describe the nature of a dative bond. For instance, sharing electrons equally from both atoms or having each atom contribute one electron is characteristic of typical covalent bonding rather than a dative bond. An external source for electrons does not apply here, as the electrons specifically come from the donor atom's lone pair.