Element #68 is Erbium. The number of the isotope, of course, is the sum of the protons + neutrons. Checking the Wikipedia article "Isotopes of erbium", it looks as if this isotope doesn't actually exists.
The isotope with 16 protons and 15 neutrons is oxygen-31.
The isotope with 25 protons and 31 neutrons is Manganese-56. It has an atomic number of 25 (protons) and a mass number of 56 (protons + neutrons), which gives it 31 neutrons.
The isotope with 15 protons, 16 neutrons, and 15 electrons is oxygen-31.
Number of protons + neutrons = mass number 26 protons + 31 neutrons 57
The isotope with 34 neutrons and 31 protons is phosphorus-65.
=31,39,31 i hate masteringchemistry, good luck
p,n =31,38 P=31 (from Periodic Table) N= 68.926-31=37.926
Phosphorus has 15 protons. Its most common isotope, phosphorus-31, has 16 neutrons.
Iron-57 is a stable isotope of iron, meaning it does not undergo radioactive decay. It has 26 protons and 31 neutrons, giving it a mass number of 57. Iron-57 is commonly used in Mössbauer spectroscopy to study the properties of iron-containing compounds.
Phosphorus has 15 protons, 15 electrons, and typically has 16 neutrons in its most common isotope, phosphorus-31.
The element is sulfur and the isotope is 16S31
Phosphorus-31 is the most common isotope. (Wikipedia)