Covalent bonds form between nonmetals

Steps:

• Identify element types: Metals form ionic bonds; nonmetals form covalent bonds.
• Check periodic table positions: W and X are metals (left side); Y and Z are nonmetals (right side).
• Determine bonding: Only nonmetal pairs share electrons covalently.
• Select pair: Y and Z fit covalent compound formation.

Why D is correct:

• Y and Z are nonmetals, which share electrons to form covalent bonds per the octet rule.

Why the others are wrong:

• A: W and X are metals, forming metallic bonds.
• B: W (metal) and Y (nonmetal) form ionic compounds.
• C: X (metal) and Y (nonmetal) form ionic compounds.

Final answer: D