Question

A monoatomic anion of unit charge contains 45 neutrons and 36 electrons. Identify the ion.

• A. $C{l}^{-}$
• B. $F^{-}$
• C. $I^{-}$
• D. $B{r}^{-}$

Answer 1

Answer: (D)

Let the monoatomic anion be $X^{-}$.Number of electrons in $X-=36$
$\therefore$ Number of electrons in monoatomic atom $(X)$
$=36-1=35$
Atomic number = number of electrons in neutral atom = number of protons in neutral atom $=35$
Mass number of monoatomic atom $(X)$ = number of protons + number of neutrons
$=35+45=80$ Hence, ion must be $B{r}^{-}$.