From the following list of ions, select an isoelectronic series and arrange them in order of increasing size.
na^+ , mg^2+, na^-, mg^+, n^3-, f^-, mg^2-, o^+, o^2-, f^+

Explanation:

An Isoelectronic Series is a group of atoms/ions that have the same number of electrons.

Na^+ , Mg^2+, N^3-, F^-, O^2- (This series each have 10 electrons.)

Arrange them in order of increasing size (increasing order of ionic radius)

Mg^2+ < Na^+ < F^- < O^2- < N^3-

   72    <   102 < 133 < 140   < 146

"standard molar enthalpy:

h2o ( liquid water ) : - 285.8 kj/mole

h2o ( water vapor ) : - 241.8 kj / mole.

δhrxn = - 241. 8 - ( - 285.8 )= -241.8 + 285.8 = 44.0

answer: 44.0 kj"