Answer: Option B. -> Constant weathering and erosion of rocks 
:
B
Soil on earth comes from rocks. The dynamic natural elements likewind, flowing rivers,change in seasons, etc areresponsible for the erosion of rocks and the formation of soil.

Answer: Option A. -> Amount of water (mL)Percolation time (mins)
:
A
Percolation rate is a measure of the water retention capacity of a soil sample. It is measured as:
Percolation rate (mL/min) = $\frac{\text{Amount of water (mL)}}{\text{Percolation time (mins)}}$

Answer: Option D. -> Soil profile
:
D
The different types of particles and substances present in soil lead to the formation of different vertical layers.Thisis called soil profile. Each individual layer has different properties and texture.

:
Part 1: 2 Marks
Part 2: 3 Marks
1)The decay of the remains of plants and animals that forms humus mostly happens on top of the soil. Therefore the humus formed remains mostly on the top soil.
2) The importance of humus is as follows:
a) Humus controls and regulates plant growth.
b) The better the humus content in the soil, the healthier and more productive the soil will be.
c)Good humus also reduces wind erosion of soil.

:
Definition: 1 Mark
Causes: 2 Marks
The contamination of soil due to excessive use of chemicals and harmful waste products like fertilizers, insecticides, industrial wastes etc. is called soil pollution.
Following are the causes of soil pollution:
1. Excessive use of chemical fertilizers
2. Waste disposal from industries
3. Mining activities

:
Statement: 1 Mark
Reasons: 2 Marks
No, it is not a good practice to remove grass and small plants that are growing in an open, unused field.
Plants cover the soil surface and their roots bind the soil particles and hold them in place. During strong winds and rains, they prevent soil erosion and thereby protect the top soil. This stops patches of land turning into deserts after long periods of time.

:
Each factor: 1 Mark
Any two:
Soil formation is influenced by the following factors:
1.Organism
2.Topography
3.Time
4.Climate
5.Parent material

:
Each difference: 1 Mark
1. Physical weathering does not change the chemical composition of the rock whereas chemical weathering changes the chemical composition.
2. Physical weathering may result due to temperature, pressure, snow, etc. whereas chemical weathering mainly takes place due to the action of some chemicals.

:
Each reason: 1 Mark
(a) This is so because of excessive use of water which depletes the ground water.
(b) Towns and cities have asphalted roads and vast areas of soil are concreted. As a result, rain water cannot percolate to recharge ground water and the ground water level decreases further. Villages have larger areas of open soil surface and fewer asphalted roads and concrete surfaces.

:
Justification: 1 Mark each
The statement is true, since each crop requires different things out of the soil and the weather around it. For example,
1. Cereals likewheat and gramare grow only inclayey and loamy soils,because these plants need the soil to have better water retention capacity.
2. Soils rich inclayand organic matter with good water retention capacity are ideal forpaddy.
3. Loamy soils, which drain water easily, are suitable forlentils and other pulses, which don't need the water to stay in the soil for a longer time.
4. Forcotton,loamy or sandy soilsare more suitable, because of their water draining and air logging capacity.
5. Wheat requires soils that are rich in humus and fertile. So clayey soils are very good for wheat.