Question

why J is the only one alphabet which is not used in periodic table?

Answer 1

Latin names are not commonly written with letter J. J was added only in modern times (much later than U), so Julius = Iulius, but classically educated people still hate "j" and would put "i" in its place at every opportunity. They don't even put letter J in latin dictionaries. Since element names are latinized, unless you have element named after some person or place that has J in its name you are not likely see a j in element name

Answer 2

may b this is ur answer
letter j is not include in periodic table bcoz many of elements r named in greek n latin languages .
in latin letter j is written as i n in greek language it is symbolises as iota.
therefore it might b reason bhind it