Which of these does not reflect the periodicity of the elements.

Which of the following does not reflect periodicity of elements ?

Which of the following does not reflect periodicity of elements ?

Which of the following is not a periodic property for the elements?

Which of the following does not exhibit the periodicity in properties of the elements?

Which of the following does not exhibit the periodicity in properties of the elements?

The modern periodic table does not explain the periodicity in properties of elements.

Which is the first element in the periodic table ?

The electronic configuration of an element 'X' is 2, 8, 8, 2. To which period and group of the periodic table does the element 'X' belong ? State its valency. Justify your answer in each case.