Answer:
118
Step-by-step explanation:
The periodic table is an arrangement of elements in rows and columns. The vertical columns are called groups while the horizontal rows are called periods.
The eighteenth group in the periodic table are called noble gases. All the elements in this group are gases. Coincidentally, the heaviest element, oganesson belongs to this group and has atomic number 118.
This element exits as a gas and it is the heaviest known gas.