which has highest second ionisation energy?

a)Na

b)Mg

c)K

d)Al

and please tell hw?

Na because it attains intert gas configuration after losing 1 electron . so as inert gases are more stable greater energy is required to remove the electron .. hope u find it useful . for more queries contact me at gogosush@gmail.com

a) Na = Ne 3s1

b) Mg = Ne 3s2

c) K    = [Ar] 4s1

d) Al  =  [Ne] 3s2 3p1

Now to compare second ionisation energy the conf. will be

a) Na = Ne

b) Mg = Ne 3s1

c) K    = [Ar]

d) Al  =  [Ne] 3s2

Now Sodium and Aluminium has achieved its stable conf. i.e noble gas conf. or now are fully filled and thus more stable than Mg and Al.

Now in K and Na,

Na will have highest second ionisation energy. neon is maller than argon considering difficult to ionize or remove electrons from Neon as compare to Argon.

plz approve!

electronic config of Na(+) is noble gas config. . so its very difficult to remove an electron so it will have very high 2nd ionisation enthalpy
in case of Mg(+) and Al(+) its not noble gas config so 2nd ionisation enthalphy will be realtively less

Now we have Na(+) and K(+)
As we know that the size of K(+) is more than that of Na(+) so ionisation enthalpy will be more for Na(+)

So 2nd ionisation enthalphy will be the highest for Na . 

Please approve 

its Na