Question

For $PdC{l_2}.4N{H_3}$, $PtC{l_2}.2N{H_3}$and $CoC{l_3}.4N{H_3}$ reacts with excess amount of $AgN{O_3}$ individually and gave $2\;mole$ of $AgCl$, zero $mole$ of $AgCl$, $1mole$ of $AgCl$ respectively. Then identify the secondary valences of $Pd$, $Pt$ and $Co$respectively.
$\left( 1 \right)\;\;6,4,7$
$\left( 2 \right)\;\;4,2,4$
$\left( 3 \right)\;\;2,2,3$
$\left( 4 \right)\;\;4,4,6$

Answer 1

Hint: We are talking about coordinated compounds here so first we should learn about coordinated compounds. Coordinated compounds are chemical compounds that contain multiple anion or neutral molecules that are connected to a central metal atom through a coordinate bond. We will discuss their valency. The central metal atom has two valencies: a primary valency and secondary valency.

Complete answer:
Let us understand the given option first, $PdC{l_2}.4N{H_3}$ is reacting with excess amount of $AgN{O_3}$ to give $2\;mole$ of $AgCl$ we can observe that for $2\;mole$ of $AgCl$ to be formed $PdC{l_2}.4N{H_3}$ must have reacted with $2\;mole$ of $AgN{O_3}$ so the remaining compound will be $Pd{\left( {N{H_3}} \right)_4}$ it contains four coordinated molecule or ligands so its secondary valency is four.
Let’s see the second option, $PtC{l_2}.2N{H_3}$ is reacting with excess amount of $AgN{O_3}$ to give zero moles of $AgCl$ we can observe that $PtC{l_2}.2N{H_3}$ did not react and no amount of product was formed so $PtC{l_2}.2N{H_3}$ remains same, as it contains four coordinated molecule or ligands so its secondary valency is four.
Let's see the third option $CoC{l_3}.4N{H_3}$ is reacting with excess amount of $AgN{O_3}$ to give $1mole$ of $AgCl$ we can observe that for $1mole$ of $AgCl$ to be formed, $CoC{l_3}.4N{H_3}$ must have reacted with $1mole$ of $AgN{O_3}$ so one chlorine is lost and now the remaining compound is $CoC{l_2}.4N{H_3}$, as it contains six coordinated groups or ligands its secondary valency is six.
So, the correct answer is option $\left( 4 \right)$.

Note:
Secondary valency of an element in a compound is the number of ion molecules that are coordinated to the element or it can be defined as the number of ligands that are attached to the element. Coordinated groups are also known as ligands.