What was one important discovery that the curies made?
a material’s radioactivity cannot be changed by altering the material physically.
a material’s radioactivity can be weakened or intensified by changing it chemically.
radioactive materials generally contain radium or polonium.
radioactive materials are found only in the form of salts.

A material’s radioactivity cannot be changed by altering the material physically.

Explanation:

Marie Curie studied the radiation of all compounds containing the known radioactive elements. She discovered that:

- The strength of uranium radiation can be exactly measured;

- The intensity of radiation is proportional to the amount of the radioactive element;

- The ability to emit radiation depends only on the interior of the atom, so it doesn't depends on the material physically.

metals are good conductor of electricity. it has free electrons on their surface. according to electron pool theory, each atom present in a metal crystal losses all of its valence electron and as a result a pool of free is form. these pool of electrons are free to move and   conduct electricity easily   while making metal as good conductor.

the correct answer is a. the ability of electrons to flow throughout the metal.

if it's not useful, feel free to report for mistake in answer.

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.