6 electrons are present in $t_{2 g}$ level and 0 electrons are present in $e_{g}$ level.
The crystal field stabilization energy of $\left[ Co \left( NH _{3}\right)_{6}\right] Cl _{3}$ is $CFSE =6 \times\left(-0.4 \Delta_{0}\right)+0 \times\left(0.6 \Delta_{0}\right)=$
$-2.4 \Delta_{0}$
$(I)\, d^3\,\,\, (II)\, d^5 \,\,\,(III)\, d^6 \,\,\,(IV)\, d^8$
કારણ : $NF_3$ આયનીકરણ કરતાં $F^-$ આયનો જલીય દ્રાવણ આપે છે.