Isotope, one of two or more species of atoms of a chemical element with the same atomic number and position in the periodic table and nearly identical chemical behaviour but with different atomic masses and physical properties.

The mass defect of a nucleus is the difference between the total mass of a nucleus and the sum of the masses of all its constituent nucleons. Mass defect is the difference between the predicted mass and the actual mass of an atom's nucleus. The binding energy of a system can appear as extra mass, which accounts for this difference.

Complete the nuclear reaction O 8 15 + n 0 1 → C 6 12 + ?

Given, O 8 15 + n 0 1 → C 6 12 + ? Equating atomic number and mass number. Atomic number of unknown element = 8 + 0 - 6 = 2 Mass number of unknown element = 15 + 1 - 12 = 4 Hence, the unknown element is He 2 4 .