Asubstance may change from one form to another with change in temperature. these are changes

Physical changes

As we know,

Physical changes are those changes which can be reversed and is not permanent. It does not change the chemical nature of the substanceA great example of physical change is given in the question itself, When a substance is melted it can be frozen or cooled back to it's original form, When an object is frozen it can be melted back to its Liquid form, and when an object is in gaseous form like water vapour it can be cooled, and brought back to liquid form

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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.