Question

The kilogram is the SI base unit of mass and is equal to the mass of the international prototype of the kilogram, a _____ standard that is kept at the International Bureau of Weights and Measures (BIPM).
A) Platinum-iridium
B) Platinum
C) Iridium
D) All of the above

Answer 1

Hint: First let us see what SI unit is:
The International System of Units (SI, abbreviated from the French International System (d'unités)) is a modern metric system. It is the only method of measurement of official status in virtually every country in the world. It consists of a coherent set of measurement units beginning with seven simple units, the second, metre, kilogram, ampere, kelvin, mole and candela.

The approach allows for an infinite number of additional units, called derived units, which can often be interpreted as products of the powers of the basic units.

Complete step by step solution:
Mass is the amount of matter in the material. More significantly, it can be both a real body property and an indicator of its resistance to acceleration when a certain level of force is applied. However, one significant thing that students can note here is that mass is distinct from weight even though the words are often used interchangeably. Also, they've got separate units.

Kilogram is used as a SI mass unit. It is defined by the $kg$ symbol.
It is known as the mass of the platinum-iridium block stored in the International Bureau of Weights and Measures in France.

Hence, The kilogram is the SI base unit of mass and is equal to the mass of the international prototype of the kilogram, a platinum-iridium standard that is kept at the International Bureau of Weights and Measures (BIPM).

Thus, option (A) is correct.

Note: Although kilogram is the standard unit of mass, there are other units of mass also gram, milligram, centigram, decagram etc.