there is an anomaly when it comes to the position of hydrogen bcz it can be placed either in group 1 or 17 in the first period .why?????????

Hydrogen shows a dual character by showing resemblance with alkali metals ( group 1) as well as halogens (group 17).Therefore, there is an anomaly when it comes to the position of hydrogen in the periodic table.

Resemblance of hydrogen with alkali metals:

1. Like alkali metals, hydrogen has only one electron in the outermost shell
2. Like alkali metals, it looses one electron to form a cation H⁺
3. Like alkali metals, it is a reducing agent
4. Like alkali metals, it combines with the electronegative elements such as halogens, oxygen etc to form corresponding compounds.

Resemblance with halogens:

1. Like halogens, hydrogen has a tendency to gain an electron and complete its outermost shell (K shell)  to achieve noble gas (Helium) configuration.
2. Hydrogen is a non-metal like halogens and is a bad conductor of heat and electricity.
3. It exists as a diatomic molecule like halogens.
4. The ionization potential of hydrogen is of the same order as halogens.
5. It combines with other non- metals like carbon, silicon etc. to form covalent compounds like halogens do.

Due to these properties of hydrogen, the position of hydrogen is anomalous although it has been placed in group 1.