Which of the following is a low spin complex?

The ammonia prepared by treating ammonium sulphate with calcium hydroxide is completely used by $NiCl_2 \cdot 6H_2O$ to form a stable coordination compound. Assume that both the reactions are $100 \%$ complete. If $1584 \ g$ of ammonium sulphate and $952 \ g$ of $NiCl_2 \cdot 6H_2O$ are used in the preparation,the combined weight (in grams) of gypsum and the nickel-ammonia coordination compound thus produced is $\qquad$ (Atomic weights in $g \ mol^{-1}: H=1, N=14, O=16, S=32, Cl=35.5, Ca=40, Ni=59$)

When a metal rod $M$ is dipped into an aqueous colourless concentrated solution of compound $N$,the solution turns light blue. Addition of aqueous $NaCl$ to the blue solution gives a white precipitate $O$. Addition of aqueous $NH_3$ dissolves $O$ and gives an intense blue solution.
$1.$ The metal rod $M$ is
$(A)$ $Fe$ $(B)$ $Cu$ $(C)$ $Ni$ $(D)$ $Co$
$2.$ The compound $N$ is
$(A)$ $AgNO_3$ $(B)$ $Zn(NO_3)_2$
$(C)$ $Al(NO_3)_3$ $(D)$ $Pb(NO_3)_2$
$3.$ The final solution contains
$(A)$ $[Pb(NH_3)_4]^{2+}$ and $[CoCl_4]^{2-}$
$(B)$ $[Al(NH_3)_4]^{3+}$ and $[Cu(NH_3)_4]^{2+}$
$(C)$ $[Ag(NH_3)_2]^{+}$ and $[Cu(NH_3)_4]^{2+}$
$(D)$ $[Ag(NH_3)_2]^{+}$ and $[Ni(NH_3)_6]^{2+}$
Give the answer for questions $1$,$2$ and $3$.

$A$ mixture $X$ containing $0.02 \, mol$ of $[Co(NH_3)_5SO_4]Br$ and $0.02 \, mol$ of $[Co(NH_3)_5Br]SO_4$ is dissolved in water to make a $2 \, L$ solution.
$1 \, L \, of \, X + \text{Excess of } AgNO_3 \rightarrow Y \, mol \, of \, ppt.$
$1 \, L \, of \, X + \text{Excess of } BaCl_2 \rightarrow Z \, mol \, of \, ppt.$
Then $Y$ and $Z$ are respectively ...............

$CuSO_{4(aq)}$ $\xrightarrow{H_2S \uparrow} M \downarrow$ $\xrightarrow[\text{Excess}]{KCN} N + O$
Then final products $N$ and $O$ are respectively.

The number of ions present in $2.0 \ L$ of a solution of $0.8 \ M \ K_4[Fe(CN)_6]$ is