Mass of manganese from MnO₂ in the ore Steps:

• 1 tonne of ore = 1000 kg; 4% MnO₂ means 0.04 × 1000 kg = 40 kg MnO₂.
• Molar mass of MnO₂ = atomic mass of Mn (55) + 2 × atomic mass of O (16) = 87 g/mol.
• Mass fraction of Mn in MnO₂ = 55/87.
• Mass of Mn = (55/87) × 40 kg ≈ 25.3 kg. Why A is correct:
• It matches the calculation using the mass fraction of Mn in MnO₂ (55/87 ≈ 0.632), applied to 40 kg of the compound. Why the others are wrong:
• B is the full mass of MnO₂ (40 kg), ignoring oxygen removal.
• C approximates double the Mn mass (≈63 kg), possibly confusing with 2 moles.
• D is close to twice the MnO calculation (≈62 kg), using wrong formula (MnO instead of MnO₂).

Final answer: A