Step-by-step explanation:
To help us determine which element results from the reaction between NH3 and BF3, we can identify the valence states of the atoms that participate in the reaction and how many bonds they can form.
We have for each element the valence electrons and the bonds that they can form in such a way that they complete 8 electrons in the last energy level:
*N ---> 3 valence electrons, can form maximum 5 bonds
*H ---> 1 valence electrons, can form maximum 1 bond
*B ---> 5 valence electrons, can form maximum 3 bond
*F ---> 9 valence electrons, can form maximum 1 bond, if it lose one electron
Now we compare the options they give us with the maximum possible links that each element can form.
A and B have a hydrogen atom that forms two bonds, this is not possible since it does not have enough electrons to do so. So we discard A and B.
In C we have a fluorine atom forming two bonds, this is not possible since it can only form a bond by donating its electron.
Option D has the correct links for each element, so the answer will be D.
Answer: D