A first-order reaction has a half-life of 20.0 minutes. Starting with 1.00 x 10^20 molecules
of reactant at time t = 0, how many molecules remain unreacted after 100.0 minutes?
A) 1.00 x 10^4molecules
B) 2.00 x 10^19 molecules
C) 3.20 x 10^16 molecules
D) 5.00 x 10^20 molecules
E) none of the above