Which option describes a similarity and a difference between isotopes of an element?
a) same atomic number; different number of protons
b) same number of protons; different atomic number
c) same atomic number; different mass number
d) same mass number; different atomic number
e) same number of neutrons; same number of protons

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.