How many elements have been found to be essential for plants?

An element must be considered essential,when
$I.$ the element is necessary for supporting normal growth and reproduction of the plants
$II.$ the deficiency of that particular element can not be met by supplying some other element
$III.$ the element is directly involved in the metabolism of the plants. Choose the correct pair

Which one of the following is $NOT$ an essential mineral element for plants?

Which of the following elements is not essential for plant growth?

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?

Which one is not an essential element in plants?