Questions from Inside the chapter

Class 9
Chapter 1 Class 9 - Matter In Our Surroundings

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

The order of densities is as follows

Iron > Chalk > Honey > Water > Exhaust from chimneys > Air

Explanation:

We know that,

• Particles in solids are packed tightly
• Particles in liquids are packed with some space between them
• Particles in gases have more space between them.

So in a fixed volume, the number of particles would be greatest in solids, followed by liquids and then gases.

So,

Density of Solid > Density of Liquid > Density of Gas.

Now,

• Air is Gas
• Exhaust from air has particles, so it has more mass
• Water is liquid
• Honey is semi-solid, so heavier than water
• Chalk is a sold, but lighter than iron

Thus, we write

Iron > Chalk > Honey > Water > Exhaust from chimneys > Air

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