Covalent compounds form between nonmetals Steps:

• Examine the periodic table diagram to classify W, X, Y, Z as metals or nonmetals based on position.
• Metals are on the left; nonmetals on the upper right.
• Covalent bonding occurs when nonmetals share electrons.
• Select the pair both classified as nonmetals.

Why D is correct:

• Y and Z are nonmetals (e.g., groups 15-17), which form covalent compounds by sharing valence electrons, as defined by the octet rule.

Why the others are wrong:

• A: W and X are metals (e.g., groups 1-2), forming metallic bonds, not covalent.
• B: W is a metal and Y a nonmetal, forming ionic compounds via electron transfer.
• C: X is a metal and Y a nonmetal, forming ionic compounds.

Final answer: D