Answer:
the stem, but if its more specific xylem cells
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 :

Calcium carbon oxygen, calcium chlorine , carbon hydrogen oxygen, hydrogen chlorine, calcium oxygen hydrogen. pretty sure they’re right
<span>a pure substance that can be separated into different elements by chemical means</span>