With reference to soil,what does the term 'critical element' mean?

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 of the following is not essential for all plants?

In which of the following,all three are macronutrients?

Elements present in plant tissues in concentrations less than $..........$ are called micronutrients.

Which of the following elements is not required by plants for their normal healthy growth?