well in order to answer this question you have to provide more information < 3
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.
4d^55s^1 ( third choice)
on passing the small ampere of electric current through the tube made of ar and hg of cfl generates uv rays which excites the fluorescent and thus emits the high radiation by consumption of just 5- 12 w in comparison to incandescent light which requires more power such as around 40 - 55 w to lighten.
moreover the life span of fluorescent or cfl is around 8000 h whereas the life span of incandescent is around 1200 h
hence, the building installed with incandescent lights bears more electricity bill.