Symbols <ιμγωιδτη=∀115∀ηειγητ=∀32∀σρχ=∀2−χηαπτερ_φιλεσ/ιμαγε014.πνγ∀> can be written, whereas symbols <ιμγωιδτη=∀117∀ηειγητ=∀32∀σρχ=∀2−χηαπτερ_φιλεσ/ιμαγε015.πνγ∀> are not acceptable. Answer briefly.

The general convention or method of representing an element along with its atomic mass [A] and atomic number [Z] followed globally is ^A_ZX. Atomic number of an element is fixed. However, mass number is not fixed as it depends upon the isotope taken. Hence it is essential to indicate mass number.