he given isotope is bismuth 208. The atomic number of bismuth is 83 therefore the number of protons is 83. When bismuth loses one proton it results in the element lead with only 82 protons. The mass number is the total number of protons and the total number of neutrons. So on losing proton bismuth becomes lead and on gaining neutron the mass number does not change and remains as 208. Therefore it reduces to lead but the mass number remains the same.
Therefore the answer is B. Bismuth on losing one proton and on gaining a neutron it becomes Lead 208.
