The correct options are
A Cis and trans forms are not diastereomers to each other
D It has three optically active isomers:
d,l and trans forms
(A) Two geometrical isomers are possible for the complex
[CrCl(NO2)(en)2]+ cis and trans.
In the cis isomer, two ethylene diamine ligands are adjacent and in the trans isomer, they are opposite.
Thus statement A is true.
(B) Cis and trans forms are diastereomers to each other.
Thus statement B is not true.
(C) Only the cis isomers display optical activity. Whereas trans isomer is optically inactive.
Thus statement C is true.
(D) Cis isomer has two optically active isomers: d, l form. The trans form is optically inactive.
Thus statement D is not true.
Hence, the correct options are B and D