Read the entire Procedure for the Introductory Activity. In step 5, why is it necessary to make sure the stopcock is in the open position and then immediately replace the stopper and syringe assembly in the Erlenmeyer flask after adding the hydrochloric acid to the marble chips

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.

im pretty sure its b