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 :

- The difference between single displacement reaction and double displacement reaction are:
Explanation:
in the chemical reaction an atom in a molecule is replaced by another atom forming the end product .this type of chemical reaction involved only two reactants for example zinc + copper sulphate give us copper sulphate + copper.double displacement reaction is the reaction in which two compounds react together to form two other compounds by mutual exchange of other ions is called double displacement reaction.this type of reaction is involved two or more than two reactants.for example AG and O3 + NaCl give us agcl + nano3
by classifying into categories that get smaller and smaller these are the classification steps : life , domain , kingdom , phylum , class, order , family , genus , and species every time you narrow it down the option gets smaller and smaller till there's none left except the species it self .
Answer:
c. crystallization
Explanation:
The opposing process that occur in a solution in contact with undissolved solute are dissolution and crystallization.
In the dissolution process the solid substance coverts into liquid state and mixes with solution. Whereas in Crystallization the the chemical is converted from the liquid solution to solid crystal state.