Which of the following is a spin-free complex?

The correct increasing order of trans-effect of the following species is:

Copper sulphate solution reacts with $KCN$ to give

Cold ferrous sulphate solution on absorption of $NO$ develops brown colour due to the formation of

For the reaction given below:
$CoCl_{3} \cdot xNH_{3} + AgNO_{3(aq)} \rightarrow$
If two equivalents of $AgCl$ precipitate out,then the value of $x$ will be $....$

The stepwise stability constants of a complex are given below. What is its overall reaction stability constant $\beta_4$ ?
$M + L \rightleftharpoons ML ; K_1 = 1.0 \times 10^4$
$ML + L \rightleftharpoons ML_2 ; K_2 = 1.0 \times 10^3$
$ML_2 + L \rightleftharpoons ML_3 ; K_3 = 1.0 \times 10^3$
$ML_3 + L \rightleftharpoons ML_4 ; K_4 = 1.0 \times 10^2$
(Overall reaction : $M + 4L \rightleftharpoons ML_4$)