To determine which compounds contain no covalent bonds, we first need to understand what a covalent bond is. A covalent bond is formed when two atoms share one or more pairs of electrons. This typically occurs between non-metal atoms. In contrast, ionic bonds are formed by the complete transfer of electrons from one atom to another, usually between a metal and a non-metal.

Let's analyze each compound step by step:

Step 1: Analyze KCl
Potassium (K) is a metal and chlorine (Cl) is a non-metal. KCl is formed by the transfer of an electron from K to Cl, resulting in an ionic bond. It does not contain any covalent bonds.

Step 2: Analyze PH₃
Phosphine (PH₃) consists of phosphorus (P) and hydrogen (H), both non-metals. The bonds are formed by sharing electrons, so they are covalent bonds.

Step 3: Analyze O₂
Oxygen gas (O₂) is a diatomic molecule with two oxygen atoms (non-metals) sharing electrons, so it has a covalent double bond.

Step 4: Analyze B₂H₆
Diborane (B₂H₆) has boron (B) and hydrogen (H), both non-metals. It contains covalent bonds, including some unique 3-center-2-electron bonds, but all are covalent in nature.

Step 5: Analyze H₂SO₄
Sulfuric acid (H₂SO₄) has hydrogen, sulfur, and oxygen, all non-metals. The bonds within the molecule (S-O, O-H) are covalent.

From this analysis, only KCl has no covalent bonds; it is purely ionic. All other compounds involve covalent bonding.

Final Answer: KCl

Related Topics and Formulae

Ionic Bond: Formed by electrostatic attraction between oppositely charged ions. Example: $\mathrm{KCl}\to K^{+}+{\mathrm{Cl}}^{-}$

Covalent Bond: Formed by sharing of electron pairs. Example: $H:O:H$ in water (H₂O).

Key Theory: Metals and non-metals typically form ionic bonds, while non-metals with non-metals form covalent bonds. Some compounds can have both ionic and covalent characteristics (polar covalent bonds), but in this case, KCl is purely ionic.