Ncert Exercises & Solutions

Which pair of ions has the same electronic configuration?

1.	$Cr^{3+}, Fe^{3+}$	2.	$Fe^{3+}, Mn^{2+}$
3.	$Fe^{3+}, Co^{3+}$	4.	$Sc^{3+}, Cr^{3+}$

Hint: Draw the electronic configuration of each ion and check the same configuration

The electronic configuration of ions is as follows:

{}_{24}{Cr} = [Ar] 3 d^{5}, 4 s^{1}

${}_{24}{Cr} = [Ar] 3 d^{5}, 4 s^{1}$

{}_{26}{Fe} = [Ar] 3 d^{6}, 4 s^{2}

${}_{26}{Fe} = [Ar] 3 d^{6}, 4 s^{2}$

{}_{25}{Mn} = [Ar] 3 d^{5}, 4 s^{2}

${}_{25}{Mn} = [Ar] 3 d^{5}, 4 s^{2}$

{}_{27}{Co} = [Ar] 3 d^{7}, 4 s^{2}

${}_{27}{Co} = [Ar] 3 d^{7}, 4 s^{2}$

{}_{21}{Sc} = [Ar] 3 d^{1}, 4 s^{2}

${}_{21}{Sc} = [Ar] 3 d^{1}, 4 s^{2}$

{}_{24}{Cr}_{3 +} = [Ar] 3 d^{3}

${}_{24}{Cr}_{3 +} = [Ar] 3 d^{3}$

{}_{26}{Fe}_{3 +} = [Ar] 3 d^{5}

${}_{26}{Fe}_{3 +} = [Ar] 3 d^{5}$

{}_{25}{Mn}_{2 +} = [Ar] 3 d^{5}

${}_{25}{Mn}_{2 +} = [Ar] 3 d^{5}$

{}_{27}{Co}_{3 +} = [Ar] 3 d^{6}

${}_{27}{Co}_{3 +} = [Ar] 3 d^{6}$

{}_{21}{Sc}_{3 +} = [Ar]

${}_{21}{Sc}_{3 +} = [Ar]$

Thus, Fe³⁺ and Mn²⁺ have the same electronic configuration.