Which of the following is $NOT$ an essential mineral element 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

In plants,mineral nutrients are classified into macronutrients and micronutrients. On what basis is this classification made?

The most abundant element present in plants is

Macronutrients like carbon,hydrogen and oxygen are obtained mainly from

Explain with examples: macronutrients,micronutrients,beneficial nutrients,toxic elements and essential elements.