I think the toaster was invented in 1910
The atomic number is the simply the number of protons in the atom. So in the first row with atomic number 2, the number of protons is 2.
If the atom has no charge, which I think you can assume for all of these, the number of electrons is equal to the number of protons. So the number of electrons is also 2.
The number of neutrons (which are the particles with no charge in the nucleus) is simply the mass number minus the atomic number i.e. 4 - 2 = 2.
The isotopic symbol is the symbol which is found on the periodic table of elements. There are 2 numbers associated which each element on the table. The larger is the mass number and the smaller is the atomic number. The atomic number or number of protons is what identifies the element. Looking at the periodic table ( https://sciencenotes.org/wp-content/uploads/2015/01/PeriodicTableOfTheElementsBW.pdf or https://simple.wikipedia.org/wiki/Periodic_table_(big) ), it can be seen that the element on the first row above with an atomic number of 2 is Helium with a symbol He. The number that is included with the name is simply the mass number which is 4 in this case, which tells us that this type of helium has 2 neutrons.
Another type (or isotope) of helium is Helium-3 which has one neutron.
Try the next row and post back if you have trouble with it
Answer:
Explanation:
Polyatomic ions are ions that contain more than one atom in each one of the ions.
Ionic compounds are made of cations (positive ions) and anions (negative ion). By convention, the cation is written before the anion.
List the ions in each compound:
<h3>CaCO₃</h3>
Cation: 
,
Anion: 
.
is a monatomic ion for it contains only one atom in each ion.
is a polyatomic ion for it contains four atoms (one C atom and three O atoms) in each ion.
<h3>NaF</h3>
Cation: 
,
Anion: 
.
Both and are monatomic for they contain only one atom in each ion.
<h3>FeO</h3>
Cation: 
,
Anion: 
.
Both and 
are monatomic for they contain only one atom in each ion.
<h3>CaCl₂</h3>
Cation: ,
Anion: 
.
Both and 
are monatomic for they contain only one atom in each ion.
<h3>NaOH</h3>
Cation: ,
Anion: 
.
is a monatomic ion for it contains only one atom in each ion.
is a polyatomic ion for it contains two atoms (one O atom and one H atom) in each ion.
Guess I recommend doing that
