Answer:
Valence electrons or outer electrons are most important as they participate in bonding. The octet rule states that atoms gain, lose, or share valence electrons to have filled energy levels.. this gives atoms a stable configuration like that of the nearest noble gas.
Answer:
16.06 L was the initial volume of the balloon.
Explanation:
Initial moles of freon in ballon = 
Initial volume of freon gas in ballon = 
Moles of freon gas added in the balloon = n = 3.50 mole
Final moles of freon in ballon = 
Final volume of freon gas in ballon = 
Using Avogadro's law:
( at constant pressure and temperature)

16.06 L was the initial volume of the balloon.
The balanced equation for the reaction is as follows
Na₂CO₃ + 2HCl --> 2NaCl + CO₂ + H₂O
stoichiometry of Na₂CO₃ to HCl is 1:2
number of Na₂CO₃ moles reacted = molarity x volume
number of Na₂CO₃ moles = 0.100 mol/L x 0.750 L = 0.0750 mol
according to molar ratio of 1:2
1 mol of Na₂CO₃ reacts with 2 mol of HCl
then 0.0750 mol of Na₂CO₃ mol reacts with - 2 x 0.0750 = 0.150 mol
molarity of given HCl solution is 1.00 mol/L
molarity is defined as the number of moles of solute in 1 L of solution
there are 1.00 mol in 1 L of solution
therefore there are 0.150 mol in - 0.150 mol / 1.00 mol/L = 0.150 L
volume of HCl required is 0.150 L