Emeka carried out a reaction in which a gas was given off. He followed the progress of the reaction by measuring the mass of the reaction vessel over time. After 5 minutes the mass of the reaction vessel
had decreased from 120g to 114.5g. Calculate the rate of this reaction.

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)

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.