Answer:
The mass number is defined as the total number of protons and neutrons in an atom. The number of neutrons = mass number − atomic number.
The standard state formation reaction is a chemical reaction in which one moles of substance in its standard state is formed from its constituent element in their standard state.All the substance must be in their most stable state at 100kpa and 25 degrees celsius.
therefore for HF is
1/2H2 +1/2F2 =HF
iodine which should appear before tellurium and argon which should appear after potassium
There is a 3rd one: nickel should appear before cobalt
There are seven periods with eighteen columns in the periodic table.
