Possible isomers -
$(i)$ Geometrical isomers
$(ii)$ In trans form plane of symmetry present, so trans form is optically inactive but cis is optically active
Total number of stereoisomer $=2+1=3$
(આપેલ પરમાણુ ક્રમાંક $: V, 23; Cr, 24, Fe, 26 Ni, 28)$
$V ^{3+}, Cr ^{3+}, Fe ^{2+}, Ni ^{3+}$