Reason1: electrons on farther layers become free easyer 2nd reason: volume of atoms grows (from Helium to Xeon) so instead of boyle-mariot law equation (PV=vRT) is more accurate to use van der walls equations that adds to the boyle-mariot equation the volume occupied by the atoms of the gas to the volume of the space between the atoms P(Vm-b)=vRT
Writing electronic configuration of any element you should know atomic number of that element ,
and also electrons are filling according to their energy level and first electron is filled in the lower energy orbital
and it follows n+1 rule if n+1 is same for two orbital electron will go first in the lowest value of n.
writing electronic configuration of ion can be done like first for their neutral atom and then add or remove electron it will make things easy because there are also some eception case their you may do wrong.
pH is the measure of alkalinity or acidity of a compound.
pH = - log [H+]
and pH + pOH = 14
where pOH is the measure of basicity of a solution, given by -log[OH-]
As a solution gets more basic that is higher [OH-], the pH increases, and on the other hand, as the pH of a solution decreases by one pH unit, the concentration of H+ increases by ten times.