I believe that in developed nations, the nutrients that are most lacking in a child's diet are the; calcium, iron and zinc. Zinc is needed for the activity of more than 100 different enzymes in the body and plays a role in the immune function. It aids in the maintenance of healthy immune function in kids and may reduce the frequency of mild upper respiratory tract infections. Calcium keeps the bones healthy and teeth thus supporting the skeletal structure and function. Iron is an important component of hemoglobin.
        
             
        
        
        
These organisms convert nitrogen in the soil to ammonia, which can then be taken up by plants. This process also occurs in aquatic ecosystems, where cyanobacteria participate. After nitrogen has been fixed, other bacteria convert it into nitrate, in a process known as nitrification.
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Answer:
Magnesium, calcium, phosphorous, sulfur these are essential nutrients for plants. These are required in trace quantity but are very important for plant life. Point A. will be correct answer.
Explanation:
As in B. starch n cellulose are composed of only carbon, oxygen and hydrogen.
As in C. These elements are not required on special occasion but are necessary throughout plant life.
As in D.  C H N O  is the primary component plants need but these secondary nutrients are equally necessary for growth n structure of plant.
<u><em>So answer A. Is the correct option.</em></u>
Calcium plays the most important role in structure formation of plants. Also act as messenger molecule in signaling. Deficiency  of calcium caused wilting , weakened stem and ultimately death of plant.
Magnesium is the key element in chlorophyll molecule. It is necessary for chlorophyll formation.
Sulfur is another very important element in plant life, it is necessary for protein synthesis in plants.
Phosphorous plays an important role in  process of cell devision , photosynthesis and respiration.
Potassium is very crucial in gaseous exchange ,it operates the opening and closing of stomata. 
 
        
             
        
        
        
Answer:
The correct statements are C The pH is accurate but the solution will have excess salt. D The pH is accurate but the concentration of Tris will be incorrect 
Explanation:
As the pH is finally maintained at 7 the pH for the buffer solution will be accurate but excess salt will be produced due to use of Both NaOH and HCl to make up the to 7.
As more volume of water is required at final step to make up the volume the concentration of tris will be incorrect.