(a)In an experiment on soil porosity, the following measurements were taken and recorded: Volume of dry soil = 50 cm³, Volume of water = 50 cm³, Total volum...

(a) Soil porosity experiment.

Given: volume of dry soil = 50 cm\(^3\); volume of water added = 50 cm\(^3\); total volume of soil and water together = 75 cm\(^3\).

When the water is poured onto the dry soil, it fills the air spaces (pores) between the soil particles. If there were no air spaces, the combined volume would have been \(50 + 50 = 100\) cm\(^3\). Because the actual combined volume is only 75 cm\(^3\), the water has occupied the pore (air) spaces.

(i) Volume of air space = (volume of soil + volume of water) \(-\) total volume

\[ = (50 + 50) - 75 = 100 - 75 = 25 \text{ cm}^3 \]

(ii) Porosity = \(\dfrac{\text{volume of air space (pore space)}}{\text{volume of soil}} \times 100\)

\[ = \frac{25}{50} \times 100 = 50\% \]

(b) Three reasons why soil porosity is important:

1. It allows aeration, supplying oxygen to plant roots and soil organisms.
2. It controls the movement, drainage and retention of water in the soil.
3. It promotes root penetration and the free movement of soil air, water and micro-organisms, aiding plant growth.

(c) Four characteristics of each rock type:

Igneous rocks:

1. Formed by the cooling and solidification of molten magma or lava.
2. They are hard, crystalline and non-porous.
3. They contain no fossils.
4. They occur in massive form and are not arranged in layers (non-stratified); examples are granite and basalt.

Sedimentary rocks:

1. Formed by the deposition, compaction and cementation of sediments (weathered rock particles).
2. They are usually soft and often porous.
3. They frequently contain fossils.
4. They are arranged in layers (stratified); examples are limestone and sandstone.