The isotope of iodine with mass number 131 is often used in medicine as a radioactive tracer. write the symbol for this isotope indicating both mass number and atomic number.

Iodine - 113, means iodine with mass number 113

To specify a particular isotope, add superscript and subscript on the left of symbol.

The superscript indicates the mass number (number of protons + neutrons)

The subscript indicates the atomic number (number of protons)

The iodine - 113 is writen

113

I [this the letter i]

53

superscript 113 on the left ofd the symbol is the mass number = protons + neutrons

I is the symbol (letter i)

subscript 53 on the left of the symbol is the atomic number (number of protons)