Relative density of a substance is expressed by comparing the density of that substance with the density of:

1. air
2. mercury
3. water
4. iron

The unit of relative density is:

1. g cm^-3
2. kg m^-3
3. m³ kg^-1
4. no unit

The relative density of silver is :

1. 11.7
2. 9.5
3. 12.8
4. 10.5