Adevice for measuring atmospheric pressure is a

Barometer

The device used in meteorology to measure atmospheric pressure is called a barometer. It consists of a long glass tube filled with mercury and turned upside down into a container of mercury. The tube is closed at one end and open at the other which works by balancing the mercury in the glass tube against the outside air pressure. As air pressure increases, the air becomes heavier and it pushes more of the mercury up into the tube. As air pressure decreases, mercury drains from the tube. 

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.