Answer: Option B. -> China, Australia, Brazil, India
Answer: (b)

Answer: Option D. -> France and Russia
Answer: (d)

Answer: Option C. -> Nickel, Zinc, Copper, Aluminium
Answer: (c)

Answer: Option A. -> excess irrigation
Answer: (a)
Soil salinity is the salt content in the soil; the process of increasing the salt content is known as salinization.
Excess irrigation leads to an increase in soli salinity since water is absorbed by plants and salts are left behind in the soil and eventually begin to accumulate. Salination from irrigation water is also greatly increased by poor drainage and the use of saline water for irrigating agricultural crops.

Answer: Option A. -> Chernozem soils
Answer: (a)
Chernozem or black earth variety of soil is rich in organic matter in the form of humus. It is generally a modified type of loess.
True chernozem is black in colour, but there are various grades, shading off into a grey and chestnut-brown soils. It forms in areas that have cold winters, hot summers, and rapid evaporation of precipitation; generally, only tall grass is found native to chernozem.

Answer: Option D. -> Second
Answer: (d)

Answer: Option A. -> Only 1 and 3
Answer: (a)

Answer: Option D. -> Mauritius
Answer: (d)

Answer: Option C. -> Keystone species
Answer: (c)

Answer: Option D. -> Congo basin - Negrito
Answer: (d)