Which of the following is a characteristic of unit?(1) Must be universally accepted.(2) Must be well defined and invariable.(3) Easily available and suitable size.(4) All the above.

The correct answer is (4) All the above.

Here's why:

(1) Must be universally accepted: For a unit to be effective, it must be universally accepted. This means that it is recognized and used by everyone, regardless of their location or culture.

(2) Must be well defined and invariable: A unit must be well defined so that there is no ambiguity about what it represents. It must also be invariable, meaning it doesn't change over time or under different conditions.

(3) Easily available and suitable size: A unit should be easily available, meaning it can be easily accessed and used by everyone. It should also be of a suitable size, meaning it is not too large or too small for the quantity it is used to measure.

Therefore, all of the above characteristics are important for a unit.