Question

First oinisation enthalpy of sodium is lower than that of magnesium

Answer 1

yes first ionisation enthalpy of sodium is less than that of magnesium
first ionization enthalpy means the energy required to remove one outermost electron from the valence shell
as in case of sodium(11)
e- configuration is
2,8,1
so after removal of 1 e- it stabilises by acquiring noble gas configuration
but for magnesium(12)
e- configuration is
2,8,2
so it will acquire noble gas configuration only after removal of 2 e-
so it is easy to remove 1 e- from sodium
than magnesium