The SI unit of mass, the kilogram, is currently defined A) as 10^-22 the mass of the Earth's moon. B) as 10^-24 the mass of the Earth. C) by a prototype platinum-iridium cylinder kept at the International Bureau of Weights and Measures in Sevres, France. D) the mass of 5.9786332 × 10²⁶ protons. E) by the President's weight.

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The kilogram was historically defined by a platinum-iridium prototype cylinder, known as the International Prototype Kilogram (IPK), which was kept at the International Bureau of Weights and Measures in Sevres, France. However, it's important to note that as of May 20, 2019, the definition has been updated to be based on the Planck constant, but the choice provided here reflects the historical definition prior to this change.

The SI Unit of Mass, the Kilogram, Is Currently Defined