Which of the following elements could not find a fixed place in Mendeleev's periodic table?

1. A key limitation of Mendeleev's table was the placement of hydrogen. 2. Hydrogen resembles both alkali metals (group I) and halogens (group VII), so no single fixed position fit it. 3. Hence hydrogen could not be assigned a fixed place. _Source: RRB Group D CEN-02/2018 PYQ, Q.74._