Click on the diagram to choose which atom is more reactive. Hint: These are nonmetals. Which is going to gain a full valence shell of 8 electrons the easiest?

The first one has 5 valence electrons, and the second has 7. (This can be counted by counting the amount of black dots on the biggest circle). Since 7 > 5, it would be easier for the second one to gain one (so that it completes it's valence shell) so the answer is the second one.

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.