Question

In which of the following reactions is hydrogen undergoing oxidation?

• A. $2H_2+O_2\to 2H_{2}O$
• B. $2HCl\to H_2+C{l}_2$
• C. $H_2+F_2\to 2HF$
• D. $Zn+H_{2}S{O}_4\to ZnS{O}_4+H_2$

Answer 1

Answer: (A), (C)

The correct options are
A

$2H_2+O_2\to 2H_{2}O$

C

$H_2+F_2\to 2HF$

Let us look at all the options and see the change in oxidation number for hydrogen in all the cases. The oxidation number is given on top of every atom in the reaction.

(1) $2H_2^0+O_2^0\to 2H_2^{+1}{O}^{-2}$, Since oxidation number of hydrogen is increasing from 0 to +1 we can say that oxidation of hydrogen occurs in this reaction.

(2) $2H^{+1}C{l}^{-1}\to H_2^0+C{l}_2^0$, Since oxidation number of hydrogen is decreasing from +1 to 0 we can say that reduction of hydrogen occurs in this reaction.

(3) $H_2^0+F_2^0\to 2H^{+1}{F}^{-1}$, Since oxidation number of hydrogen is increasing from 0 to +1 we can say that oxidation of hydrogen occurs in this reaction.

(4) $Z{n}^0+H_2^{+1}{S}^{+4}{O}_4^{-2}\to Z{n}^{+2}{S}^{+4}{O}_4^{-2}+H_2^{+1}$, Since oxidation number of hydrogen is decreasing from +1 to 0 we can say that reduction of hydrogen occurs in this reaction.

So the correct answers are $2H_2+O_2\to 2H_{2}O$ and $H_2+F_2\to 2HF$.