Which statements about complex IV are true? 1) This complex catalyzes the reduction of oxygen to water. 2) Despite consuming protons, this complex pumps H+ across the membrane at a rate of 4 per molecule of O2 reduced. 3) The protons flow across a gradient to the inner membrane space. 4) Conformational changes as electrons flow through the complex alter the ability of some residues to bind protons.

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.