Question

Complex X of composition $Cr(H_{2}O{)}_{6}C{l}_n$ has a spin only magnetic moment of 3.83 BM. It reacts with $AgN{O}_3$ and shows geometrical isomerism. The $IUPAC$ nomenclature of X is

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• A. Tetraaquadichloridochromium (III) chloride dihydrate
• B. Dichloridotetraaquachromium (IV) chloride dihydrate
• C. Tetraaqadichloridochromium (IV) chloride dihydrate
• D. Hexaaquachromium (III) chloride

Answer 1

The correct option is A Tetraaquadichloridochromium (III) chloride dihydrate

Complex : $Cr(H_{2}O{)}_{6}C{l}_n$

Spin only magnetic moment = $\sqrt{n(n+2)}BM$
$=\sqrt{3.8}BM$

n= no. of unpaired electrons

$\therefore$ $n=3$
$\therefore Cr$ is in $+3$ oxidation state
Complex is $Cr(H_{2}O{)}_{6}C{l}_3$
This formula have following isomers

(a) $\left[Cr\right(H_{2}O{)}_6]C{l}_3$ : react with $AgN{O}_3$ but does not show geometrical isomerism.
(b) $\left[Cr\right(H_{2}O{)}_{5}Cl]C{l}_2.H_{2}O$ react with $AgN{O}_3$ but does not show geometrical isomerism.
(c) $\left[Cr\right(H_{2}O{)}_{4}C{l}_2]Cl.2H_{2}O$ react with $AgN{O}_3$ & show geometrical isomerism.
(d) $\left[Cr\right(H_{2}O{)}_{3}C{l}_3].3H2O$ does not react with $AgN{O}_3$ & show geometrical isomerism.
(e) $\left[Cr\right(H_{2}O{)}_{4}C{l}_2]Cl.2H_{2}O$ react with $AgN{O}_3$ & show geometrical isomerism.

$\therefore \text{Complex is}\left[Cr\right(H_{2}O{)}_{4}C{l}_2]Cl.2H_{2}O$

$IUPAC$ name : Tetraaquadichloridochromium(III) chloride dihydrate