Question

The oxidation number of \[Cr\] in \[Cr{O_5}\] is:
A. \[ + 10\]
B. \[ + 8\]
C. \[ + 6\]
D. \[ + 4\]

Answer 1

Hint:Oxidation number is the oxidation state of the elements in any state of existence. It is an integer which can be positive, zero or negative.

Complete answer:
Oxidation number of an atom is defined as the number of electrons shared by it with other atoms. The count of the number of electrons shared in a bond by an atom gives the oxidation number.
Oxidation number is positive by losing electrons and it is negative by gaining electrons. The loss of electrons is referred to as oxidation and the gain of electrons is labeled as reduction. The oxidation number of an atom is dependent on the electronegativity of the atom.
Oxidation number or oxidation state of an atom or ion is determined by the using the number of shared electrons by the bonded atoms. The summation of all the constant oxidation states of other bonded atoms are taken together and then equated with the charge of the molecule or ion.
The given molecule is a compound of chromium. Chromium is an element in the periodic table with atomic number \[24\] and electronic configuration\[\left[ {Ar} \right]3{d^5}4{s^1}\] . Thus chromium atoms can show a maximum valency of \[6\] by losing six electrons.
The \[Cr{O_5}\]​ molecule contains one chromium central atom which is bonded to five oxygen atoms. One of the four oxygen atoms is bonded to chromium by a double bond. The other four oxygen atoms are linked to chromium atoms by single peroxide linkages. Thus the oxidation number of oxygen which is double bonded is \[ - 2\] and the oxidation number of oxygen atom which is bounded by peroxide linkages is\[ - 1\] . Let, \[x\] is the oxidation number of \[Cr\] which is bonded to five oxygen atoms.
Thus \[x + \left( { - 2} \right) + 4\left( { - 1} \right) = 0\]
$x = + 6.$
Therefore, the correct option is C.

Note:
The oxidation number is very important for identifying the chemical change of a transformation. The redox reactions have considerable change in oxidation states of reactants and products.