What is the isotope symbol for an atom that contain 82 protons and 125 neutrons?

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Answer 1 · 2018-05-18T00:20:50

#""_82^207Pb# or just #""^207Pb#.

The isotope of an element #X# is given by #""_Z^AX#, where #Z# is the proton number of the element and #A# is the mass number of the element.

The mass number of this isotope will be #82+125=207# units, while it has #82# protons.

Looking on the periodic table, element number #82# is lead, and its symbol is #Pb#.

Therefore, the isotope in this case will be written as:

#""_82^207Pb#

Alternatively, we can write it even shorter like this,

#""^207Pb#

since we know that lead can only have an atomic number of #82#.