Terrestrial vertebrates use the urea cycle to convert the ammonium ion to urea, which can then be excreted. In the production of urea, only one of the nitrogens in the product comes from an ammonium ion. What is the source of the other nitrogen in urea?

aspartate

Explanation:

Aspartic acid, is an α-amino acid that is used in the biosynthesis of proteins. Similar to all other amino acids, it contains an amino group and a carboxylic acid.

"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"

4d^55s^1 ( third choice)