Your answer is B because elements within the same column have equal numbers of valence electrons which determines the reactivity of an element.
Mass is not created or destroyed
Similarities between Mendeleev's periodic and Modern periodic table: Elements are arranged in groups and periods. Elements with similar properties are placed in the same group. Metals and non-metals are placed separately.
The major difference is that the elements in Mendeleev's periodic table were arranged by atomic mass and the modern periodic table arranges elements by atomic number. Of course as elements are constantly being discovered there were significantly fewer elements in Mendeleev's periodic table.
