Q52. The total number of species from the following in which one unpaired electron is present, is $\_\_\_\_$\\
$\mathrm { N } _ { 2 } , \mathrm { O } _ { 2 } , \mathrm { C } _ { 2 } ^ { - } , \mathrm { O } _ { 2 } ^ { - } , \mathrm { O } _ { 2 } ^ { 2 - } , \mathrm { H } _ { 2 } ^ { + } , \mathrm { CN } ^ { - } , \mathrm { He } _ { 2 } ^ { + }$\\