Which of the following elements is incorrectly placed in Mendeleev's periodic table?

Compounds of which elements(s) were used as a standard referemce by Mandeleev's to classify elements?

What is the total number of triads identified by Dobereiner?

Modifications of which of the following arrangements of elements resulted into the formation of the modern periodic table ?

Why is Newland's method of classification of elements known as the Law of Octaves?

To which of the following elements is Newland laws of Octave not applicable?

The element 'eka - Aluminium' predicted by Mandeleev is____________.

Which of the following elements is placed along with cobalt in the same slot in Mendeleev's periodic table?

At which element, Newland's arrangement of elements ended?
 

In case of the triad containing Ba, Ca and Sr, elements,  which of the following statements is correct?