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 $=2+1=3$
Column $-I\,-$ Column $-II\,-$ Column $\,-III$
$(P)\, Fe(CO)_5\,\,\, (Q)\,CO\,\,\, (R)\, H_3B \leftarrow CO\,\,\,(S)\, [Mn(CO)_5]^-$