Which of the following complexes will not show optical isomerism?

Among the following complexes,the one that can exhibit optical activity is

Which isomer of $CrCl_3 \cdot 6H_2O$ is green in color and reacts with $AgNO_3$ to form one mole of $AgCl$?

$Fac$ and $Mer$ isomerism is associated with which of the following general formula?

Amongst the following ions,which one has the highest magnetic moment value?
$(i)$ $[Cr(H_2O)_6]^{3+}$
$(ii)$ $[Fe(H_2O)_6]^{2+}$
$(iii)$ $[Zn(H_2O)_6]^{2+}$

The correct order of the calculated spin-only magnetic moments of complexes $A$ to $D$ is:
$A$. $Ni(CO)_{4}$
$B$. $[Ni(H_{2}O)_{6}]Cl_{2}$
$C$. $Na_{2}[Ni(CN)_{4}]$
$D$. $PdCl_{2}(PPh_{3})_{2}$