Answer: 8.1 days
Explanation:
Expression for rate law for first order kinetics is given by:

where,
k = rate constant
t = age of sample
a = let initial amount of the reactant = x
a - x = amount left after decay process=
a) to find rate constant
Half life is the amount of time taken by a radioactive material to decay to half of its original value.


b) for completion of one fourth of reaction



Thus after 8.1 days , one fourth of original amount will remain.
A.) Periods within the periodic table. :)
<span>The principal quantum number for the highest energy electron in carbon would be 2. It is easy to spot this, since carbon exists in row 2 of the period table. The row in which an element resides always shows the highest value of n, or the principal quantum number, that an electron can reside in.</span>