Symbols 79 35Br and 79Br can be written, whereas symbols 35 79 Br and 35Br are not acceptable. Answer briefly.

Symbols and can be written, whereas symbols are not acceptable. Answer briefly.
Answer
The general convention of representing an element along with its atomic mass (A) and atomic number (Z) is
 Hence, is acceptable but is not acceptable. can be written but cannot be written because the atomic number of an element is constant, but the atomic mass of an element depends upon the relative   abundance of its isotopes. Hence, it is necessary to mention the atomic mass of an  element