The condition(s) essential for a unit to be accepted internationally : (1) The unit should be of convenient size and without any ambiguity. (2) The unit should be reproducible. (3) The value of the unit should not change with space and time. (4) All of the above.

All of the above

Reason — The condition(s) essential for a unit to be accepted internationally are :

1. The unit should be of convenient size.
2. It should be possible to define the unit without any ambiguity.
3. The unit should be reproducible.
4. The value of a unit should not change with space and time.