Question

In Mendeleev's periodic table, gaps were left for the elements to be discovered later. Which of the following elements found a place in the periodic table later?
A.Germanium
B.Chlorine
C.Oxygen
D.Silicon

Answer 1

Hint: Elements were grouped in Mendeleev's periodic table according to their fundamental property, atomic mass, and chemical properties. Just 63 elements were identified during Mendeleev's time. Mendeleev discovered that the properties of elements were bound to atomic mass in a periodic way after observing their properties. He grouped the elements in the periodic table such that elements with identical properties were in the same vertical columns.

Complete answer:
Mendeleev's periodic table contains some gaps with elements that were unknown at the time.
In 1869, Dmitri Mendeleev published the first periodic table of chemical elements, based on properties that emerged with some regularity as he arranged the elements from lightest to heaviest. Mendeleev observed gaps in the periodic table when he suggested it and predicted that then-unknown elements with properties sufficient to fill such gaps existed. With atomic masses of 44, 68, 72, and 100, he called them eka-boron, eka-aluminium, eka-silicon, and eka-manganese.
Eka-boron (Eb, under boron, B, 5), eka-aluminium (Ea or El, under Al, 13), eka-manganese (Em, under Mn, 25), and eka-silicon (Es, under Si, 14) were found to be good predictors of the properties of scandium (Sc, 21), gallium (Ga, 31), technetium (Tc, 43), and germanium (Ge, 32)
Hence option A is correct
The element germanium was later added to Mendeleev's periodic table, taking the place of Eka–silicon.

Note:
Mendeleev considered formulae of hydrides and oxides to be one of the most basic requirements for categorization among chemical properties. He took 63 cards and wrote the properties of one element on each one. He pinned the elements that had identical properties together on the wall. He saw that elements were grouped in increasing order of atomic mass, and that elements with identical properties appeared on a regular basis.
He proposed a periodic law based on this finding, stating that “the properties of elements are the periodic property of their atomic masses.”