The SI (International system of units) unit of length is ______.

metre

The correct answer is option 1. metre.

The SI (International System of Units) unit of length is metre.

The metre (symbol: m) is the base unit of length in the International System of Units (SI). It is defined as the length of the path travelled by light in a vacuum during a time interval of 1/299,792,458 of a second. The metre is commonly used to measure distances, lengths, and dimensions in various scientific and everyday contexts.