The brown ring test for $NO_2^-$ and $NO_3^-$ is due to the formation of a complex ion with the formula:

Aluminium trifluoride is insoluble in anhydrous $HF$ but dissolves on addition of $NaF$. Aluminium trifluoride precipitates out of the resulting solution when gaseous $BF_3$ is bubbled through. Give reasons.

Complex $A$ has a composition of $H_{12}O_{6}Cl_{3}Cr$. If the complex on treatment with conc. $H_{2}SO_{4}$ loses $13.5\%$ of its original mass,the correct molecular formula of $A$ is :
[Given : atomic mass of $Cr = 52 \ amu$ and $Cl = 35.5 \ amu$]

In which of the following complexes is the radius of $Fe$ the largest?

Choose the correct statements from the following:
$A$. Ethane$-1, 2-$diamine is a chelating ligand.
$B$. Metallic aluminium is produced by electrolysis of aluminium oxide in the presence of cryolite.
$C$. Cyanide ion is used as a ligand for the leaching of silver.
$D$. Phosphine acts as a ligand in Wilkinson's catalyst.
$E$. The stability constants of $Ca^{2+}$ and $Mg^{2+}$ are similar with $EDTA$ complexes.
Choose the correct answer from the options given below:

When $100 \ mL$ of $0.2 \ M$ solution of $CoCl_3 \cdot x NH_3$ is treated with excess of $AgNO_3$ solution,$3.6 \times 10^{22}$ ions are precipitated. The value of $x$ is $\left(N_A = 6 \times 10^{23} \ mol^{-1}\right)$