Question

When methane is burnt in oxygen to produce Co2 and H20 , the oxidation no.of carbon changes by.....?

Answer 1

The oxidation number carbon will be changed from -4 to +4.
When methane is burnt in the presence of oxygen, carbon dioxide and water are produced. The equation for this reaction is given below.
CH4  +   2O2 ⇒ CO2  + 2H2O  
Being exothermic reaction, energy also produced by this reaction.
Here, carbon oxidation number changed from -4 to +4.

Moreover, Water molecules produced usually in the form of water vapors or steam.

Hope this will help you.

Answer 2

Oxidation number of hydrogen is +1
Let Oxidation number of Carbon in CH4 be x
We know, Total oxidation number of compound is neutral
According To Problem
x + (+1)*4 = 0
=>x + 4 = 0
=>x= -4

Oxidation number of C in CH4 is -4

Let Oxidation number of C in CO2 be y
Oxidation number of Oxygen is -2
According To Problem
y + 2 * (-2)=0
=>y - 4 = 0
=>y=4

Oxidation number of C in CO2 is +4
Change in oxidation number on burning CH4 to produce CO2 and H2O is
                                                                = 4 - (-4)
                                                                = +8(Ans)