Answer:
1 g
Explanation:
The half-life of Am-242 (16 h) is the time it takes for half of it to disappear.
We can make a table of the mass left after each half-life.

The mass remaining after 48 h is 1 g.
This question is asking for an element with 5 valence electrons. Just go to the row it is in (excluding transition metals) and count over.
The answer would be c. P
Let the acid be HA.
The chemical formula for this acid will be the following:

The formula for the <span>acid dissociation constant will be the following:
</span>
![K_a= \dfrac{[H^+][A^-]}{[HA]}](https://tex.z-dn.net/?f=K_a%3D%20%5Cdfrac%7B%5BH%5E%2B%5D%5BA%5E-%5D%7D%7B%5BHA%5D%7D)
<span>
We know [H+]=0.0001 (it's given).
However, we must find [A-] and [HA] in order to solve for the constant.
We find that [A-]=[H+] by using a electroneutrality equation.
Also, we can create a concentration equation to find [HA].
</span>
![0.5M=[A^-]+[HA]](https://tex.z-dn.net/?f=0.5M%3D%5BA%5E-%5D%2B%5BHA%5D)
![[HA]=0.5M-[A^-]](https://tex.z-dn.net/?f=%5BHA%5D%3D0.5M-%5BA%5E-%5D)
<span>
Now, we can find the acid dissociation constant.
</span>
![K_a= \dfrac{[H^+][A^-]}{0.5M-[A^-]}](https://tex.z-dn.net/?f=K_a%3D%20%5Cdfrac%7B%5BH%5E%2B%5D%5BA%5E-%5D%7D%7B0.5M-%5BA%5E-%5D%7D)
I think it’s B but not 100% sure