How many geometrical isomers are possible for [Cr(NH₃)2Cl₄]^{- ?
For octahedral [Ma₂b4], 2 geometrical isomers exist: cis (two NH₃ adjacent) and trans (opposite). This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Chemistry Textbook for Class XI and XII, Chapter: Some Basic Concepts, Structure of Atom and Periodicity, Topic: Mole concept, atomic models and periodic trends.