Why is hydrogen placed in group 1 and other times in group 17?

Hydrogen is placed in group 1 of the periodic table because it has one electron in its outer shell, similar to the other elements in group 1 (alkali metals). However, hydrogen also exhibits some properties similar to the halogens in group 17, such as the ability to form a -1 oxidation state by gaining an electron. This dual nature of hydrogen has led to some debate among scientists about its placement in the periodic table. Ultimately, hydrogen is typically placed in group 1 because its properties more closely align with the alkali metals.