Which of the following elements has a controversial placement in modern periodic table?

The correct option is C Hydrogen
Hydrogen can gain one electron and can become ${\text{H}}^{-}$ ion just like halogens in group 17 can form ${\text{X}}^{-}$ ion. Also, it can lose an electron and can become ${\text{H}}^{+}$ ion just like alkali metals in group 1 can form ${\text{M}}^{+}$ ion. Hence, the position of hydrogen is controversial in the modern periodic table.