Question

Covalency for central atom is maximum in:
A.$B{F_3}$
B.$S{O_2}C{l_2}$
C.$POC{l_3}$
D.$BeC{l_2}$

Answer 1

First we have to know the covalency of an atom is the number of bonds an atom forms within a given molecule or compound. To find the covalency, we need to draw the Lewis structure (Chemical structure) of the given molecule and count the number of bonds or the number of shared electron pairs.

Complete answer:
The chemical structure of $B{F_3}$ is

In $B{F_3}$, the boron atom forms $3$ bonds with Fluorine. So, covalency $B{F_3}$ is $3$.
The chemical structure of $S{O_2}C{l_2}$ is

In $S{O_2}C{l_2}$, the sulphur atom forms $4$ bonds with oxygen and $2$ bonds with chlorine. So, covalency $S{O_2}C{l_2}$ is $6$.
The chemical structure of $POC{l_3}$ is

In $POC{l_3}$, the phosphorus atom forms $2$ bonds with oxygen and $3$ bonds with chlorine. So, covalency $POC{l_3}$ is $5$.
The chemical structure of $BeC{l_2}$ is

In $BeC{l_2}$, the beryllium atom forms $2$ bonds with chlorine. So, covalency $BeC{l_2}$ is $2$.
Hence the correct option is (B) $SO_2​Cl_2$​.

Note:
Note that the combining capacity of an atom or a molecule is known as its valency. The valency of an element in a molecule is equal to the number of electrons present in the outermost shell and if it is greater than 4, then the valency of an element is determined by subtracting the total number of electrons present in the outermost shell from eight. If the number of electrons in the outer shell is between one to four, the compound is said to have positive valency.