Question

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

• A. $Cl^-$
• B. $F^-$
• C. ${I^-}$
• D. $Br^-$

Answer 1

Answer: (D)

$Br^-$

Answer 2

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 $Br^-$.