Areactant or is being consumed in a first-order reaction. what fraction of the initial r is consumed in 4.0 half-lives

Answer : If a reactant undergoes first order kinetics and the initial reactant was R is consumed in 4 half lives then,

the first half life would undergo from 1 to 1/2R; 

the second half life will go from 1/2R to 1/4R;

in third half life it will undergo from 1/4R to 1/8R;

And finally in fourth half life it will go from 1/8R to 1/16R.

So, it means is utilized and only 1/16 R remains

The correct answer is b