Concept:Hydrogen exhibits properties similar to both alkali metals and halogens, so it can conveniently be placed in two different groups in the periodic table.
Explanation:Hydrogen has one valence electron, just like the alkali metals in Group 1.
It can lose this electron to form a positive ion,
H+.
This behaviour is similar to alkali metals such as lithium and sodium.
Hydrogen also resembles halogens because it can gain one electron to form
H−, the hydride ion.
Moreover, hydrogen exists as a diatomic molecule,
H2, just like halogens such as
F2 and
Cl2.
Because of this dual behaviour, hydrogen is sometimes placed in Group 1 (alkali metals) and sometimes in Group 17 (halogens).
No other element among the given options shows such convenient placement in two groups.
Answer:C. Hydrogen