An unknown gas has a density of 1.98 g/L. Calculate its molar mass and determine what gas it is from the table.
gas
molar mass
carbon dioxide
44
oxygen
32
nitrogen
28
helium
4
oxygen
O carbon dioxide
nitrogen
O helium

the seeing the electronic configuration we can say that the element is fluorine.

fluorine is the most electronegative element in the periodic table.

but by only seeing the configuration we cannot say about its reactivity because we don't know if its configuration after excitation or by addition of electrons.

but if not then, it is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. as the most electronegative element, it is extremely reactive: almost all other elements, including some noble gases, form compounds with fluorine.