Element X exhibits mixed bonding typical of group VI nonmetals

Steps:

• HX is covalent, so X shares electrons with hydrogen, indicating a nonmetal.
• NX is covalent, so X shares electrons with nitrogen, confirming nonmetallic character.
• NaX is ionic, so X accepts one electron to form a stable X⁻ anion with sodium.
• Group VI elements match this pattern of covalent bonds with nonmetals and ionic monovalent salts with metals.

Why D is correct:

• Group VI elements form covalent HX (e.g., H₂O approximated as HX) and NX (e.g., NO), and ionic NaX (e.g., NaOH as NaX), per valence electron configuration allowing -1 ions.

Why the others are wrong:

• A. Group II metals form only ionic compounds like Na₂X, not covalent HX or NX.
• B. Group III elements form trivalent ions or covalent networks, not simple NaX.
• C. Group IV elements like carbon form tetravalent covalent compounds exclusively, no ionic NaX.

Final answer: D