Agood experimental design should always

A good experimental design should always BE REPEATABLE.

When scientists report the results of their investigations, other scientists always critically examined their works in order to confirm if the results obtained are valid or not. To accomplish this, other scientists have to carry out the experiment just the same way that the original investigator carried it out. This implies that, it is very important for scientists to design their experiments in such a way that it will be very easy for other scientists to copy and reproduce. Scientific experimental set ups must be repeatable.

i'm assuming that the correct answer is indeed the first one/ "a"..

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.