The number of geometrical isomers for $[Co(NH_3)_3(NO_2)_3]$ is ....

Which of the following complex ions is expected to absorb visible light?
[At. nos. $Zn = 30$,$Sc = 21$,$Ti = 22$,$Cr = 24$]

Which of the following complexes will not show optical isomerism?

The number of isomers possible for the square planar complex $K_2[PdClBr_2(SCN)]$ is

$A$ chromium complex with a formula $CrCl_3 \cdot 6H_2O$ has a spin-only magnetic moment value of $3.87 \ BM$ and its solution conductivity corresponds to a $1:2$ electrolyte. $2.75 \ g$ of the complex was dissolved and passed through a cation exchanger. The solution obtained after the process was reacted with excess $AgNO_3$. The amount of $AgCl$ formed in the above process is . . . . . . $g$. (Nearest integer) [Given: Molar mass in $g \ mol^{-1}$: $Cr = 52, Cl = 35.5, Ag = 108, O = 16, H = 1$]

Explain optical isomerism.