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

The formula of the complex formed in the ring test for $NO_2^-$ and $NO_3^-$ is .....

$CuSO_4$ solution reacts with excess of $KCN$ solution to form:

$CrCl_3 \cdot xNH_3$ can exist as a complex. $A$ $0.1 \ m$ aqueous solution of this complex shows a depression in freezing point of $0.558^{\circ} C$. Assuming $100 \%$ ionisation of this complex and that the coordination number of $Cr$ is $6$,the complex will be: (Given $K_f = 1.86 \ K \ kg \ mol^{-1}$)

Silver chloride dissolves in excess of ammonium hydroxide solution. The cation present in the resulting solution is

Assign $A, B, C, D$ for the type of observation in the following reaction:
$CuSO_4 + KCN \text{ (excess)} \longrightarrow K_3[Cu(CN)_4] + \frac{1}{2}(CN)_2$