The percent by mass of copper in cap c u cap b r sub 2 is Use percent Element is equal to total mass of element in compound over molar mass of compound times 100

CuBr₂ contains 1 copper atom and 2 bromine atoms. Its molar mass is 63.55 + 2(79.90) = 223.35 g/mol, so copper’s mass percent is (63.55 ÷ 223.35) × 100 ≈ 28.45%. Therefore, the correct choice is 28.45 percent.

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