Question ATPL - Airline Transport Pilot license - Mass and Balance

83 - ATPL - In mass and balance calculations the 'index' is:

An imaginary vertical plane or line from which all measurements are taken.

A location in the aeroplane identified by a number.

The range of moments the centre of gravity (cg) can have without making the aeroplane unsafe to fly.

Is a figure without unit of measurement which represents a moment.