Ionic bonds lead to highest melting points among these substances

Steps:

• Classify each substance by bonding type: ammonia and methane are nonpolar/polar molecular, water is polar molecular with hydrogen bonding, sodium chloride is ionic.
• Recall that ionic compounds require more energy to melt due to strong electrostatic attractions between ions.
• Compare approximate melting points: ammonia (-78°C), methane (-182°C), water (0°C), sodium chloride (801°C).
• Identify sodium chloride as having the highest value based on bonding strength.

Why C is correct:

• Sodium chloride is an ionic compound; its high melting point (801°C) follows Coulomb's law, where strong attractions between Na⁺ and Cl⁻ ions demand significant heat to overcome.

Why the others are wrong:

• A. Ammonia: Molecular compound with weak intermolecular forces, melts at -78°C.
• B. Methane: Nonpolar molecular with only London dispersion forces, melts at -182°C.
• D. Water: Polar molecular with hydrogen bonding, but still melts at 0°C, far below ionic solids.

Final answer: C