The oxidation number of C in HCN and HNC respectively are ______.

A. + 2, + 2

B. + 2, + 4

C. + 4, + 4

D. - 2, - 2

To determine the oxidation numbers of carbon in hydrogen cyanide (HCN) and hydrogen isocyanide (HNC), we need to analyze the molecular structure and the bonding of each compound. Let's break it down step by step.

Understanding HCN

In hydrogen cyanide (HCN), the structure consists of a hydrogen atom (H), a carbon atom (C), and a nitrogen atom (N) arranged linearly. The carbon is bonded to the hydrogen and triple-bonded to the nitrogen. To find the oxidation state of carbon, we can use the following rules:

• The oxidation state of hydrogen is typically +1.
• The oxidation state of nitrogen in this case is -3, as it is more electronegative than carbon.

Let’s set up the equation based on the overall charge of the molecule, which is neutral (0):

Oxidation state of H + Oxidation state of C + Oxidation state of N = 0

Substituting the known values:

+1 + x - 3 = 0

Solving for x (the oxidation state of carbon):

x - 2 = 0

x = +2

Analyzing HNC

Now, let’s look at hydrogen isocyanide (HNC). The structure is similar, but the arrangement of atoms is different. In HNC, carbon is still bonded to hydrogen, but it is now bonded to nitrogen with a single bond. The nitrogen atom is also bonded to a carbon atom with a lone pair, which affects its oxidation state.

• The oxidation state of hydrogen remains +1.
• The oxidation state of nitrogen in this case is typically -3, as it is still more electronegative than carbon.

Using the same approach as before, we set up the equation:

+1 + y - 3 = 0

Solving for y (the oxidation state of carbon):

y - 2 = 0

y = +2

Final Results

Thus, the oxidation number of carbon in both HCN and HNC is +2. Therefore, the answer to the question is:

Option A: +2, +2

In summary, both compounds feature carbon with an oxidation state of +2, despite their different structures. This illustrates how the arrangement of atoms can influence the oxidation states, but in these cases, they remain the same for carbon.