Hint: You could first explain what exactly these physical quantities are. Then you could think of how a unit of this physical quantity can be defined. You could also add all the required information about the units. Then you could give the basic characters of a unit that makes it a good unit.
Complete answer: In the question, we are asked what the meaning of ‘unit’ of a physical quantity is. We are asked to list down the requirements that qualify a unit as a ‘good unit’. We know that a physical quantity is that property of a material or a system that can be measured. We normally express this measurement with a numerical value which gives the magnitude along with a unit. So, we see that this numerical value and unit are two significant characteristics of a measurement. Units are actually the standardized values. For example, one among the units of length is meters and we could also add prefixes to this unit as per the requirement to make it more precise. Units help the scientific community and even the common men in easily expressing and comparing the measured value of a physical quantity. The metric system or the SI system and the imperial system are the two systems that we use for making the measurements. There are no good units and bad units, but there are certain characteristics that are expected from a unit, like, it should be precise and clear. There should be some reference source to which we could compare the unit with.
Note: Meter, kilogram, seconds, ampere, etc are some of the known fundamental units. The metric system does support the usage of prefixes that denotes the order of magnitude. The derived units are the ones that are expressed as the combination of these fundamental units. Inter conversion of units is also possible with the help of conversion factors.