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 :

Look I am not even close to a genius in this type of stuff but the leaves help collect energy and sunlight for the plant to live off of during the winter. It basically needs them for processing and helping them with their food. Also food is stored in every pine needles mitochondrion or the powerhouse of their cell structure. In the mitochondrion their is things like chloropasts. These are like the energy or food for the cell. So when the tree cant draw nutrients from its roots or soil anymore all the excess things stored in the pine needles will help the tree survive.
Answer:
Lichens can be used as air pollution indicators, especially of the concentration of sulphur dioxide in the atmosphere. Lichens are organisms that grow in exposed places such as rocks or tree bark. They need to be very efficient at absorbing water and nutrients to grow there.
The answer is B. 6CO2+H2O yields C6H12O6+ 6H20.