Relative atomic mass of diatomic fluorine uses molecular mass halved

Steps:

• Define A_r as the average mass of element atoms relative to 1/12 the mass of a carbon-12 atom.
• Recognize fluorine exists as F₂ molecules, so measured mass is for molecules, not isolated atoms.
• Calculate atomic mass by dividing average molecular mass by 2, since each F₂ contains two F atoms.
• Complete gaps: (1) as "molecule" and (2) as "divided by 2" to yield average mass of one F atom.

Why B is correct:

• B fills (1) with "molec" (molecule) and (2) with "1/" (indicating /2), matching the formula A_r(F) = M_r(F₂)/2 for diatomic elements.

Why the others are wrong:

• A: "Atom 1/" ignores diatomic structure, incorrectly implying no division factor for fluorine.
• C: "Molecu 1/" misspells "molecule" and likely misapplies the division, not specifying /2 clearly.
• D: "Molecu 1/" same misspelling and division error as C, failing to properly halve the molecular mass.

Final answer: B