Why is pure silicon a poor conductor at room temperature? a. its valence electrons are held tightly within a crystal structure. b. it is a metal. c. it is a nonmetal. d. its valence electrons are held loosely by a positive nucleus.

The appropriate answer is a. it's valence electrons are held tightly within the crystal structure. Metals are good conductors because they share electrons and so they are free to move about enabling it to be a good conductor. Any substance that has electrons tightly held within bonds will not be good conductors. If the structure of pure silicon had its valence electrons held loosely by a positive nucleus then it would be able to conduct.

the catch is that the top numbers are atomic masses the bottom numbers are the numbers of protons and electrons in an uncharged atom. they are the number of that atoms as you would find them on the periodic table. further, the numbers on the left are used to determine the missing numbers on the right

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer

The answer is 65.3312