What is the upper fixed point (boiling point of water) on the Reamur scale?

The Reamur scale uses a specific range for its temperature divisions. Option A (40°R) is incorrect — 40°R on the Reamur scale equals 50°C, which is well below the boiling point of water. It has no special significance as a fixed point. Option B (60°R) is incorrect — 60°R equals 75°C, still below the boiling point of water. This is not the upper fixed point on any standard temperature scale. Option C (80°R) is CORRECT — the upper fixed point (boiling point of pure water) on the Reamur scale is 80°R. The Reamur scale has exactly 80 equal divisions between 0°R (freezing of water) and 80°R (boiling of water). 80°R = 100°C = 212°F = 373.15 K. The scale was proposed by René Antoine de Réaumur in 1730 and was widely used in France, Germany, and Russia before the Celsius scale became universal. Option D (100°R) is incorrect — 100 is the total number of divisions in the Celsius scale, not the boiling point in the Reamur scale.