This is the correct option. Julius von Sachs, in 1860, demonstrated the technique of hydroponics.

This is the correct option as this statement is false because prominent symptom of manganese toxicity is the appearance of brown spots surrounded by chlorotic veins.

Yes, it is correct. If the amount of essential elements is less than the amount of nutrients required for normal growth and development of plants, the level is mentioned as critical concentration.

Yes, it is correct. Both 'a' and 'c' are the bacteria which carry out the process of denitrification.

Yes, it is correct. Fe, i.e. iron, is present in a small amount in tissues. It is one of the micronutrients.

Photosynthesis is not a part of nitrogen cycle.

Pseudomonas converts nitrate salts into free nitrogen gas in nitrogen cycle. This process is known as denitrification.

Calcium is a macronutrient. It is an essential part of the plant cell wall and helps in the transport and retention of other elements.

Zinc can be absorbed by foliage. Zinc deficiencies can affect plant by stunting its growth, decreasing number of tillers, chlorosis and smaller leaves, increasing crop maturity period, spikelet sterility and inferior quality of harvested products.

Nitrogenase enzyme is present in the root nodules of leguminous plants, which helps in the conversion of atmospheric free nitrogen into ammonia.

Chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green colour of leaves, chlorotic leaves are pale, yellow or yellow-white. 

In a young root, the region of absorption of water and mineral salts is the same. 

Ash of a plant indicates which element is essential and in what amount it is necessary for a particular plant.

The mineral elements which are required by plants in a very small quantity are called trace elements. 

Plants require 16 essential elements. Essential means that these nutrients must be present for proper crop development. If not available, the plant will eventually die. Not all elements are essential. Flouride and iodine, for example, are two chemical elements which have no value for plant growth. 

Root hair forms an important surface over which plants absorb most of their water and nutrients. They are found only in the zone of maturation and not in the zone of elongation.

Plants absorb soil minerals in the form of a very dilute solution. 

At field capacity, the soil contains capillary and hygroscopic water. Field capacity is the amount of soil moisture or water content held in the soil after excess water has drained away and the rate of downward movement has decreased. 

The easily available soil water for plants is called chesard. It is utilised by a plant for its growth and functions.

Effective nodules are formed by effective strains of rhizobium. They are well-developed and pink-coloured due to the presence of a pigment called leghaemoglobin.