Question

Assertion: Oxidation number of carbon in $C{H_2}O$ is zero.
Reason: $C{H_2}O$ Formaldehyde, is a covalent compound.
(a) Both Assertion and Reason are correct and reason is the correct explanation for assertion
(b) Both Assertion and Reason are correct but reason is not the correct explanation for assertion
(c) Assertion is correct But Reason is incorrect
(d) Both Assertion and Reason are incorrect.

Answer 1

Oxidation number of an element can be defined as the degree of oxidation of an element in a given compound. It can be understood as the number of electrons gained or lost by an atom while forming a compound.

Complete answer:
First we understand the assertion part, which says that the oxidation number of carbon in $C{H_2}O$ is zero. We can calculate the oxidation number of carbon, but we need to remember some point for calculating the oxidation number i.e. the oxidation number in a neutral molecule, the sum of the oxidation number of all atoms is zero. The oxidation number of oxygen in most compounds is $- 2$.
Now we will calculate the oxidation number of carbon in $C{H_2}O$:
Net charge on $C{H_2}O$ = (O.N of carbon) (No. of atoms of carbon) + (O.N of hydrogen) (no. of hydrogen atom) + (O.N of oxygen) (no of atoms of oxygen)
$0 = (x)(1) + ( + 1)(2) + ( - 2)(1)$
$0 = x + 2 - 2$
$0 = x$
Hence, the assertion part is correct, the oxidation number of carbon is zero.
The formal oxidation state of a carbon atom in an organic molecule depends on the covalent structure. The oxidation number is the electric charge an atom would have if the bonding electrons were assigned to the more electronegative atom. Thus the reason part is correct but not appropriate.
Hence the correct answer is option B, Both Assertion and Reason are correct but reason is not the correct explanation for assertion.

Note:
Oxidation number can be calculated using some rules, as in a $C - H$ bond the oxidation number of hydrogen is $+ 1$. For carbon bonded to a more electronegative atom, each $C - O$ bond will increase the oxidation state of the carbon by $1$. For carbon to carbon bond the oxidation number is unaffected.