Question

What is the oxidation number for lead in $PbC{{l}_{2}}$ ?

Answer 1

The net charge of $PbC{{l}_{2}}$ is 0, thus none of the elements will have a sole charge. Here, chlorine has negative charge as it has to gain one electron to become stable.

Complete answer:
Here, we have been given $PbC{{l}_{2}}$ , the net charge of the element is zero.
Oxidation number of any element is defined as the number assigned to it in a chemical combination which represents the number of electrons lost or gained by an atom of that element or the compound.
Thus, oxidation number of any element depends upon the net charge of the compound and the oxidation number of the other element.
Here, the given compound is lead chloride ( $PbC{{l}_{2}}$ ) in which the chlorine atom takes electron from the lead atom as it will make the chlorine atom more stable.
The atomic number of chlorine is 17 and the number of electrons in its outermost orbit is 7, thus it only requires one electron to be at its most stable form. Thus, it takes one electron from lead.
Now, in the compound $PbC{{l}_{2}}$ there are two chlorine atoms. As one chlorine atom gets one negative charge by gaining one electron, two chlorine atoms will get two negative charges.
But, the net charge of the given compound is zero not negative two.
Therefore it would mean that the lead atom lost 2 electrons to two chlorine atoms and made itself stable.
Therefore, the oxidation number of lead becomes +2.

Note:
Many times, if the atomic number of one element is not known, the other element helps in determining how many electron the other atom requires to give or take.