Answer:
n = Initial volume/22.4L
Explanation:
The molar concept is simply one that is used to find the Number of moles and explain the relationship it has with avogadro's number, molecular mass, molar mass e.t.c.
Now, in terms of molar mass, number of moles is given by the formula;
n = mass of the sample/molar mass
In terms of avogadro's number, number of moles is;
1 mole = avogadro's number = 6.02 × 10^(23)
Now, when dealing with ideal gases, the molar volume of an ideal gas is 22.4 L.
Now the relationship between this volume and the mole concept is that the number of moles is gotten by dividing the initial volume by this molar volume.
Thus;
n = Initial volume/22.4L
Actually your answer is correct. Your answer that you picked is correct because the basic SI unit for mass is a kilograms, so therefore your answer is 13kg which you picked.
The half-life of this radioisotope : 12 hr
<h3>Further explanation
</h3>
The atomic nucleus can experience decay into 2 particles or more due to the instability of its atomic nucleus.
Usually radioactive elements have an unstable atomic nucleus.
General formulas used in decay:

t = duration of decay
t 1/2 = half-life
N₀ = the number of initial radioactive atoms
Nt = the number of radioactive atoms left after decaying during T time
t=48 hr

The half-life :
