Optical isomerism of complex ions (F325)

A question I've come across:
Describe the types of stereoisomerism found in transition metal complexes.
Use suitable examples to illustrate your answer.
So for optical isomerism, I drew two $[Ni(en)_3]^2+$ enantiomers. (I think!)
(Ni ion with three $H_3NCH_2CH_2NH_3$ bidentates)

The marks scheme says:
(Optical) + examples (must be 3-d drawings)
Rotate plane polarised light (by same number of
degrees) in opposite directions
Non-superimposable mirror images
NB If use $H_3NCH_2CH_2NH_3$ penalise only once



Why can't I use $H_3NCH_2CH_2NH_3$? And what could I use instead? Thanks!

Please quote the question exactly, including previous parts of the same question and the markscheme.

And the formula you have written for 'en' is incorrect, they are NH2 groups.

I got the question from this question pack someone else put up so I'm not sure if it's the whole question:

Question:
Describe the types of stereoisomerism found in transition metal complexes.
Use suitable examples to illustrate your answer.
[8]
Quality of Written Communication [1]
[Total 9 marks]

Marks scheme:
(Cis/trans) + Examples (must be 3-d drawings) 2
Correctly labelled as cis and trans (allow this mark if diagrams are planar) 1
Cis has same atoms at 90° + Trans has same atoms at
180° (need reference to bond angles for mark) 1
(Optical) + examples (must be 3-d drawings) 2
Rotate plane polarised light (by same number of
degrees) in opposite directions 1
Non-superimposable mirror images 1
NB If use H3N CH2 CH2 NH3 penalise only once

Any example which show the principle of cis/trans isomerism and optical
isomerism are fine but, all diagrams must be 3-d. The shapes shown in the
previous question are allowed for octahedral or tetrahedral. For square planar
complexes used to illustrate cis/trans isomerism the following illustrations
are fine. For optical isomerism, there must be a mirror line and the isomers must
be non-superimposable object/mirror images.
M M M M

QWC – to be awarded for the correct use of scientific
terms, to include at least 3 of the following:
Cis & trans, optical, plane, polarised, non-superimposable,
mirror images, geometric, bidentate,
ligand, octahedral, square planar, tetrahedral 1

And thanks for the 'en' formula thing!
(The mark scheme has it wrong too for some reason )

The isomers are ∆ and Λ, there is a bit about it on this link:

MS got it right..it says penalise if its NH3
Just ruined the joy of thinking examiner gets things wrong too