How many moles are in 2.8x10^24 atoms of silicon?

4.65 moles of Si.

Explanation:

Let x moles of silicon contains 2.8x10^24 atoms. 6.02x10^23 atoms are present in 1 mole of Si. Therefore 2.80x10^24 atoms are present in = 2.8x10^24/6.02x10^23 = 4.65 moles of Si

substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.