[owlpower]

In which reaction does Hydrogen behave as an oxidizing agent?

   0      0          +1  -1

1)H2 + Cl2 --> 2HCl

   +2  -1    0          +3  -1

2)C2H4 + H2 -->  C2H6

   0       0            +3  -1

3)N2 + 3H2 --> 2NH3

    0        0           +1   -1

4)2Na + H2 --> 2NaH


In the second equation, oxidation number of H in H2 (0) decreases to -1 in C2H6, while oxidation number of C in C2H4 (+2) increases to +3 in C2H6. Isn't H an oxidising agent in this case? The answer given is the last equation, which is also correct. I'm lost. Isn't equation 2 valid too?

[mjc123]

Carbon and nitrogen are more electronegative than hydrogen, so in hydrogen compounds we consider them to have negative oxidation numbers, and hydrogen positive.