Molar mass from atomic structures and compound formula

Steps:

• Identify elements from atomic diagrams: X has 7 protons (nitrogen, atomic mass 14 g/mol), Z has 8 protons (oxygen, atomic mass 16 g/mol).
• Determine compound formula: X and Z combine 1:1 to form NO (nitrogen monoxide).
• Calculate molar mass: Add atomic masses of one N and one O (14 + 16 = 30 g/mol).
• Confirm one mole of NO has mass 30 g.

Why D is correct:

• Molar mass equals sum of atomic masses in empirical formula, per definition of mole (Avogadro's number of formula units).

Why the others are wrong:

• A (19g): Matches fluorine atomic mass, ignores compound formation.
• B (12g): Matches carbon atomic mass, unrelated to X or Z.
• C (23g): Matches sodium atomic mass, not involved here.

Final answer: D