In Mendeleev’s Periodic table, gaps were left for many elements. Pick any one out of them

Q. In Mendeleev’s Periodic table, gaps were left for many elements. Pick any one out of them.
A. Germanium
B. Chlorine
C. Oxygen
D. Silicon
Answer: Germanium

A. Germanium
B. Chlorine
C. Oxygen
D. Silicon
Answer: Germanium