When were the last elements formally discovered and added to the periodic table of elements?

Answer 1

2015
Four elements were formally added. They do not occur naturally but are synthesised in a laboratory. They occupy the slots in the table numbered 113, 115, 117, 118., the names being recognised in 2016 as Nihonium, Moscovium, Tennessine, and Oganesson respectively. Elements 119 and 120 are also shown in the table as a potential but as at 2020 are not yet known to have been synthesised.