Element X has two isotopes. If 72.0% of the element has an isotopic mass of 84.9 atomic mass units, and 28.0% of the
element has an isotopic mass of 87.0 atomic mass units, the
average atomic mass of element X is numerically equal to
o (72.0 - 84.9) (28.0 + 87.0)
o (72.0 x 84.9) + (28.0 x 87.0)
o (72.0 + 84.9) (28.0 + 87.0)
o (72.0 x 84.9) (28.0 x 87.0)
+
100
100

3 1/4 %

explanation:

i do not get it   at all

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.