Write the drawbacks in Mendeleev's periodic table that led to its modification.

(N/A) The drawbacks of Mendeleev's periodic table are as follows:
$(i)$ Elements with similar properties were placed in different groups,while some elements with different properties were placed in the same group. For example,alkali metals $(Li, Na, K)$ were grouped with coinage metals $(Cu, Ag, Au)$,despite their distinct chemical properties. Conversely,chemically similar elements like $Cu$ and $Hg$ were placed in different groups.
$(ii)$ In some cases,elements with higher atomic weights were placed before elements with lower atomic weights to maintain the grouping of elements with similar chemical properties. Examples include the pairs $(Ar, K)$ and $(Co, Ni)$.
$(iii)$ Isotopes were not assigned separate positions in the periodic table,which contradicts the principle of classification based on atomic weight.
$(iv)$ The position of hydrogen remained controversial,as it shows properties similar to both alkali metals and halogens.
$(v)$ The arrangement of elements in group $VIII$ into three triads lacked a clear justification.
$(vi)$ The existence of even and odd series in the $IV, V,$ and $VI$ long periods could not be explained.
$(vii)$ The periodic table did not provide a proper position for the lanthanides and actinides.