Nitrous oxide (N2O) is used as an anesthetic (laughing gas) and in aerosol cans to produce whipped cream. It is also a potent greenhouse gas. The decomposition of N2O is first order. It decomposes slowly to N2 and O2:

2N2O \rightarrow 2N2 + O2

How many half-lives will it take for the concentration of the N2O to reach 2 % of its original concentration?

Explanation:

The half life of any reaction is the amount of time it takes to consume half of the starting material.

In this scenario, the initial concentration is 100% and we are going to 2%.

100% - 50%  : First Half life

50% - 25%   : Second Half life

25% - 12.5%  : Third Half life

12.5% - 6.25% : Fourth Half life

6.25% - 3.125%  : Fifth Half life

3.125% - 1.5625%   : Sixth Half life

This means it would take about 6 half lives to reach the desired concentration.

the answer would be a

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)