Question

When methane is burnt completely, oxidation state of carbon changes from

• A. +2 to 2
• B. -4 to +4
• C. 0 to -4
• D. +4 to 0

Answer 1

Answer: (B)

Option (B)

Answer 2

For methane, $CH_4$:

$$x + 4(+1) = 0 \Rightarrow x = -4.$$

For carbon dioxide, $CO_2$:

$$x + 2(-2) = 0 \Rightarrow x = +4.$$

Thus, the oxidation state of carbon changes from -4 to +4.

In $CH_4$, carbon’s oxidation state is -4; in $CO_2$, it is +4.