The answer is A for number 1 and D for 2
True..........................................................
The amount left after 20 years = 154.15 mg
<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.
The main particles are emitted by radioactive elements so that they generally decay are alpha (α), beta (β) and gamma (γ) particles
The decay formula for isotope :

Then for t=20 years, the amount left :

Answer:
Potassium
Explanation:
In group one of the periodic table both the melting and the boiling points usually decrease down the group.
Now, down the group, it's lithium that comes first, then sodium, then potassium.
Thus, among the 3, potassium is furthermost down the group by virtue of the factor it has the highest atomic number.
Therefore, we can say that potassium has the lowest boiling point among the 3.