### Theory:

Calculation of dust particles in the air:

The dust particles present in the air at a particular place can be easily calculated with a graph sheet.
Dust particles on graph sheet
1. In a graph sheet, using a marker pen, a square of $$\text{5} \times \text{5}\ cm$$ is drawn.
2. A thin film of grease is applied to the graph sheet to serve as a dust collector.
3. Likewise, four or five graph sheets are made.
4. Each dust collector is placed in different places, and the time to collect the dust particles is scheduled.
5. After the scheduled time, the paper is removed, and the number of collected dust particles in the marked area is counted using a magnifying glass.
The mean number of dust particles in the marked area can be calculated using the formula,

$$\text{Mean} = \frac{\text{Total number of dust particles on collector}}{\text{Number of squares on collector}}$$

The calculation of dust range is done with the help of the formula,

$$Range$$ $$=$$ $$Maximum\ value\ –$$ $$minimum\ value$$

From the collected details, the recordings are tabulated in the given table format.

 Location of dust collector Mean number of dust particles per small square Range

If the collector sheets are kept on the roadside or any windy places, then the range of dust will be more. If they are kept inside closed places like buildings or houses, the range of dust will be lesser, comparatively.
Water vapour:
Have you ever noticed some water droplets on the outside of glass containing cold water in it? If not, try to notice from now.

A glass containing ice cubes or cold water will form tiny water droplets over their outer surface. This is because air contains water vapour in it.

Water droplets on the glass tumbler

When the air comes in contact with a cold surface, the water vapour present in it condenses on the glass and then drops of water appear on the outer surface.

Water droplets on the glass

Water vapour in the air plays a vital role in the process of water cycle. Water vapour rises in the air, gets cooled and condenses to form clouds that bring us rain.

Water cycle
Reference:
https://pxhere.com/en/photo/1382808