Answer : The order of density from lowest density to highest density will be:
water < air < aluminum < steel < iron < silver < gold
Explanation :
Density : It is defined as the mass contained per unit volume.
Formula for density :

From this we conclude that, the density depends on mass and volume of substance.
As we know that the density is an intensive property because it does not depend upon the amount of substance. It remains same.
That means, for every substance the density always fixed. So,
The density of iron = 7.86 g/mL
The density of gold = 19.3 g/mL
The density of steel = 7.8 g/mL
The density of water = 1.00 g/mL
The density of air = 1.29 g/mL
The density of silver = 10.5 g/mL
The density of aluminium = 2.70 g/mL
From this we conclude that, the order of density from lowest density to highest density will be:
water < air < aluminum < steel < iron < silver < gold