How many essential mineral elements have been discovered yet?

Choose the correct sentence for the essential nutrient element required by plants in the greatest amount.

The major part of the dry weight of plants is made up of ............ .

What are essential elements for plants? Give the criteria of essentiality. How are minerals classified depending upon the amount in which they are needed by the plants?

$A$ : All the diverse mineral elements found in plants are not essential for them.
$R$ : Some plants accumulate heavy and toxic minerals such as gold and selenium from the soil.

Which element is present in the highest amount in plants?