Why didn’t the older boy catch chickenpox again when his younger brother had it two years later

This must have been based around earlier than the 2000'th century because now we do something call immunization which gives your baby medicine so that the baby does not get sick. So the most reasnable answer would be that the older boy either stayed his distance from his brother and or got a shot and or medication. If this is not the right answer to your homework/work then I am sorry.

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.