How would you determine the proper number of significant figures of a liquid using a graduated cylinder

Usually you can only go one more than the cylinders markings. So, for example, if your cylinder has markings of 1 mL , then at most you can say like the liquid is at 20.5 mL. Which would be 3 figures for this.

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.