Is Litre a SI unit?

Hint: Measurement is one of the most important and fundamental concepts in science. A technique in which the properties of an object are determined by comparing them to a standard is called measurement. In other words, to ensure that our everyday measurements remain comparable and consistent worldwide the International System of Units (SI) is necessary. It is important to standardize these measurements, this helps us to keep the measurement to keep them consistent and accurate.

Complete answer:
To answer this question we need to first understand the difference between the metric units and SI units. The metric system is said to be a whole collection of units suitable for trade. So it consists of cm, dm, kl, etc. It is a kind of a royal system. The SI units such as c.g.s, or m,g,s are various kinds of a subsystem of the metric system. These are introduced to implement gauss’s LMT model
Now to answer this question whether litre is a SI unit or not. The answer is no litre is not an SI unit. The SI unit of volume is said to be cubic meters. It is defined as $1d{m^3}$ but in computations expressed in litres. But litre is commonly used unit to volume.

Note:
The SI unit is said to be an international system of measurement. It is universally used in order to avoid confusion with units. The SI units are used to describe several quantities. These quantities are divided into two. They are base and derived quantities. Base quantities are said to be the fundamental building blocks of the system. Every other unit is derived from the base units that are called as a derived unit. There are a total of seven SI Base units.