why electron gain enthalpy of noble gases is always positive

The electron gain enthalpy of noble gases is always positive because it will require a large amount of energy to add a electron(as it has completely filled orbitals).

Because as the noble gas elements having completely filled or exactly half filled electronic configuration &are very stable so the energy has to supplied by the addition of electrons hence requires large amount of positive values of electron gain enthalpies

It is so because they have fully filled orbitals and hence when an electron comes , then all other electrons provides large  hinderance  to the incoming electron and hence energy is given to compensate the repulsion and so the electron gain enthalpy of noble gases is always positive.

Electron Gain Enthalpy of Noble gases is always Positive as A large amount of  energy to add an extra electron as Noble gases have a stable Electronic Configuration i.e Their orbitals are completely filled .
 

inert gases have zero electron gain enthalpy

Give reasons- (A) ionisation enthalpy of Mg is more than Al. (B) electron gain enthalpy of flourine is less than chlorine.

bcoz noble gases have thier fulfiled outermost electronic configuration. thus they doesnot need any electron in thier higher orbitals. for for accepting electron in higher orbitals of noble gas , external energy is used to give .therefore electron gain  energy of noble gases is always positive.
 

ghjsvmsdl;khdf
 

Due to full filled and half filled electronic configuration a lot of energy is required to add electronic as a result its electron gain enthalpy is always positive

Noble gases have large positive electron gain enthalpy. This is because the extra electron is placed in the next higher principal quantum energy levels. Thus, a highly unstable electronic configuration is produced.