The electronic configuration of $Co ^{3+}$ ion
$=[A r]_{18} 3 d^{6}$
The splitting in octahedral field is shown below
$C o^{3+}=3 d^{6}\left(\right.$ or $\left.t_{2 g}^{6} e_{g}\right)$
$\therefore$ There is no unpaired electron, so it is diamagnetic in nature.
$1\, L \,of\, X + Excess\, of\, AgNO_3 \rightarrow Y\, mol\, of\, ppt.$
$1\, L\, of\, X + Excess\, of\, BaCl_2 \rightarrow Z\, mol\, of\, ppt.$
તો $Y$ અને $Z$ અનુક્રમે ............... થશે.
અહીંયા $en=$ ઈથિલીન ડાયએમાઈન