Which of the following complex ions is diamagnetic in nature?

The complex cation which has two isomers is:

The number of geometrical isomers possible in triamminetrinitrocobalt $(III)$ is $X$ and in trioxalatochromate $(III)$ is $Y$. Then the value of $X+Y$ is $....$

Among $VO_2^{+}$,$MnO_4^{-}$ and $Cr_2O_7^{2-}$,the spin-only magnetic moment value of the species with least oxidising ability is $BM$ (Nearest integer). (Given atomic number $V=23$,$Mn=25$,$Cr=24$)

In a $d^4$ low spin complex,what will be the magnetic moment $(\mu)$ in $B.M.$ if the coordination number is $6$?

$A$ 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 $g \ mol^{-1}$: $Cr = 52, Cl = 35.5, Ag = 108, O = 16, H = 1$]