Concept: A coordinate bond (also known as a dative bond) is a type of covalent bond where both shared electrons come from the same atom. This typically occurs when one atom has a lone pair of electrons and another atom has an empty orbital to accept them.

Why (D) is correct:

The carbonate ion, ${\mathrm{CO}}_3^{2-}$, consists of one carbon atom covalently bonded to three oxygen atoms. The carbon atom forms two single bonds and one double bond with the oxygen atoms. The negative charge is delocalized over the oxygen atoms. All bonds in the carbonate ion are covalent bonds (either single or double), and none of them are coordinate bonds. The carbon atom achieves an octet by sharing electrons with the oxygen atoms, and the oxygen atoms also achieve octets.

Option Analysis:

• A) ${\mathrm{NH}}_4\mathrm{Cl}$: Ammonium chloride contains an ammonium ion (${\mathrm{NH}}_4^{+}$). The ammonium ion is formed when ammonia (${\mathrm{NH}}_3$) donates its lone pair of electrons to a proton (${\mathrm{H}}^{+}$), forming a coordinate bond between nitrogen and one hydrogen atom.
• B) ${\mathrm{Na}}^{+}{\left[{\mathrm{BF}}_4\right]}^{-}$: Sodium tetrafluoroborate contains the tetrafluoroborate ion (${\mathrm{BF}}_4^{-}$). This ion is formed when boron trifluoride (${\mathrm{BF}}_3$), which is electron-deficient, accepts a lone pair of electrons from a fluoride ion (${\mathrm{F}}^{-}$), forming a coordinate bond between boron and one fluorine atom.
• C) ${\mathrm{H}}_3{\mathrm{O}}^{+}$: The hydronium ion (${\mathrm{H}}_3{\mathrm{O}}^{+}$) is formed when a water molecule (${\mathrm{H}}_2\mathrm{O}$) donates one of its lone pairs of electrons to a proton (${\mathrm{H}}^{+}$), forming a coordinate bond between oxygen and one hydrogen atom.
• D) ${\mathrm{CO}}_3^{2-}$: In the carbonate ion, all bonds are formed by mutual sharing of electrons (covalent bonds), with no single atom donating both electrons for a shared pair.

Correct Answer: (D)