How many molecules of oxygen are needed to react completely with 27.9 liters
of Iron gas?
4Fe +302-->2Fe2O3

a 5.62x10^23 molecules
b 7.45x10^23 molecules
c 6.52x10^23 molecules
d 5.99x10^23 molecules
e 5.93x10^23 molecules

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.