Which group of elements was missing from Mendeleev's original periodic table?

Besides gallium, which other elements have since been discovered those were left by Mendeleev in his Periodic Table? (Any two) 

Give any two limitations of Mendeleev's periodic classification.

Write two achievements and two anomalies of Mendeleev's periodic table.

Why do you think the noble gases are placed in a separate group? 

Write merits of Mendeleev's periodic table. 

An element $\mathrm{X}$ form an oxide ${\mathrm{X}}_2{\mathrm{O}}_3$. In which group of Mendeleev's periodic table, is this element $\mathrm{X}$.

Use Mendeleev's Periodic Table to predict the formulae for oxides of the following elements: 

$\mathrm{K}$ and $\mathrm{Al}$. 

Which of the following statement are incorrect regarding Mendeleev's periodic table?

(a) Mendeleev considered compounds formed by elements with oxygen and hydrogen.

(b) In the table Ni is placed before Co

(c) Eka-silicon in Mendeleev's periodic table is gallium

(d) The properties of the elements are periodic functions of their atomic masses.