Given that nitrogen forms three bonds with hydrogen to
make NH3, how many hydrogen
atoms do you think will bond
with an atom of phosphorous?

Three

Explanation:

Nitrogen and phosphorus are on the same group in the periodic table. Elements in the same group have similar chemical properties. This is because of the number of valence electrons that they share among each other.

 The valence electrons are the outermost shell electrons found within an atom.

Nitrogen and phosphorus can both be found on the fifth group on the periodic table.

Their oxidation state is:

Since phosphorus bonds with 3 hydrogen atoms, nitrogen will also do the same.

yes the answer is total mass in unchanged   : )