Answer:
d. One additional neutron
Explanation:
Phosphorus-32, a radioactive variant of phosphorus, possesses 15 protons and 17 neutrons.
Conversely, Phosphorus-31, the most prevalent isotope of phosphorus, contains 15 protons and 16 neutrons.
This indicates that one isotope has one more neutron than the other.
That occurs with the help of nitrogen-fixing bacteria such as rhizobium.