What happens in a reaction if it is at chemical equilibrium?

The amount of the reactant is constantly decreasing.

The ratio of the products to reactants remains constant over time.

All of the products are used up.

There are no reactants in the system.

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.