Question

What object and material were used to define the kilogram for 130 years before 2019?

Options

• Water in a glass tube

• Carbon-12 atom

• Metal cylinder of platinum-iridium

• Light wave from a laser

Answer 1

Metal cylinder of platinum-iridium

Reason:

The International Prototype of the Kilogram (IPK) was made of a highly stable platinum-iridium alloy due to its resistance to oxidation and corrosion.