The mass per unit volume of a substance is called density. (density=mass/volume). Arrange the following in the order of increasing density – air, exhaust from the chimneys, honey, water, chalk, cotton and iron.

-Pooja Sharma, Subject matter expert at Edumarz

Solution: 

• As already given in the question Density is the mass per unit area. 
• The extent or packing of matter is density. More is the mass concentrated in one unit area more is the density.
• Density is more if mass is more and volume is less per unit area.
• Denser objects will get immersed in less dense objects whereas less dense objects will float on high dense material.

Right box has more balls tightly packed compared to the left one hence the right box has more density than the left one.

1. Comparing given examples  we can say that the air has the least density since it is widely dispersed in the atmosphere having more volume.
2. Exhaust from the chimney has little more density than air because of the presence of CO2, N2 etc.
3. Cotton has more density compared to air and exhaust from chimneys since it is solid and molecules of cotton are confined in one place and not dispersed having less volume.
4. Water is in liquid state and if we place cotton or honey or chalk on water they all will get immersed in water except cotton hence water has more density than cotton but less density than chalk and honey.
5. Honey is denser than water but less dense than chalk which is solid, molecules are tightly packed and has less volume.
6. Chalk is more dense than honey and all material but less dense than iron which is the heaviest and most dense material among the examples because of the strong interatomic attractions.