The products of chemical reactions often have completely different properties than the reactants, like viscosity, boiling and melting temperatures, etc.
That is because the atoms form new and different bonds to give the products.
<u>Answer:</u> The equation to calculate the mass of remaining isotope is ![[A]=\frac{20}{10^{-0.217t}}](https://tex.z-dn.net/?f=%5BA%5D%3D%5Cfrac%7B20%7D%7B10%5E%7B-0.217t%7D%7D)
<u>Explanation:</u>
The equation used to calculate rate constant from given half life for first order kinetics:
where,
= half life of the reaction = 
Putting values in above equation, we get:
Rate law expression for first order kinetics is given by the equation:
![k=\frac{2.303}{t}\log\frac{[A_o]}{[A]}](https://tex.z-dn.net/?f=k%3D%5Cfrac%7B2.303%7D%7Bt%7D%5Clog%5Cfrac%7B%5BA_o%5D%7D%7B%5BA%5D%7D)
where,
k = rate constant = 
t = time taken for decay process
![[A_o]](https://tex.z-dn.net/?f=%5BA_o%5D)
= initial amount of the sample = 20 grams
[A] = amount left after decay process = ? grams
Putting values in above equation, we get:
![0.5=\frac{2.303}{t}\log\frac{20}{[A]}](https://tex.z-dn.net/?f=0.5%3D%5Cfrac%7B2.303%7D%7Bt%7D%5Clog%5Cfrac%7B20%7D%7B%5BA%5D%7D)
Hence, the equation to calculate the mass of remaining isotope is
Xenon and neon are elements with stable configuration because they are noble gases and have enough to fill their outermost (valence) electron shell. Boron, however, only has 3 electrons in its valence shell, meaning that it is not stable and it needs to gain more electrons to be so. Calcium is an alkali earth metal and has only two electrons in its outermost shell, it will likely lose those two electrons to become stable because it takes less energy than gaining 6. Krypton and argon are other noble gases and have enough electrons to fill their shells. Helium has enough to fill it's outermost shell with 2 due to special properties of that element, it is still a noble gas. Essentially, your answer is D. If you take a look at the periodic table, you'll find your answers out in less time than it took me to type this out. All stable gases, with the exception of hydrogen, are in the last group, usually labeled as "18" but called 8 or 0.
