Question

Oxygen gas reacts with hydrogen to produce water. The reaction is represented by the equation: $O_2(g)+H_2(g)\to H_2O(g)$
the above reaction is an example of,
a) Oxidation of hydrogen
b) Reduction of oxygen
c) Reduction of hydrogen
d) Redox reaction
A. a , b , c
B. b , c , d
C. a , c , d
D. a , b, d

Answer 1

In the above reaction oxygen reacts with hydrogen to form a water molecule. The overall reaction is the combination of half-cell reaction at anode and cathode. A half cell reaction is either an oxidation or reduction reaction and it occurs in an electrochemical cell in which the electrons are lost at anode through oxidation and consumed at cathode through reduction.

Complete step by step answer:
to get the solution of above mentioned question we have to first under the following points; a. oxidation – oxidations means loss of electron, it may be defined as the chemical process in which a substance gains oxygen or loses electron and hydrogen.
Oxidation of hydrogen; the formation of ${H_2}$ is a reduction process as the two released hydrogen get together. Reaction may be written as - ${H_2} \rightleftharpoons 2{H^ + } + 2{e^ - }$ .
Reduction – reduction of gain of electrons, it may be defined as the process in which a substance loses oxygen or gains electrons and hydrogen .
Reduction of oxygen; oxygen atoms undergo reduction formally gaining electrons.
Reaction may be given as - ${O_2} + {e^ -} \to O_2^ -$
Hence the overall reaction can be written as - $2{H_2} + {O_2} \to 2{H_2} O$
In the above reaction we can see that the oxidation state of ${H_2}$ increases from zero to +1 which implies an increase in oxidation state which is oxidation of hydrogen.
And the oxidation state of oxygen decreases from zero to – 2 which implies reduction of oxygen.
And oxidation of hydrogen and reduction of oxygen occurs simultaneously hence the above reaction is an example of redox reaction.

So, the correct answer is Option D.

Note: Generally electrodes are of two types’ cathode and anode. Their sign changes according to the cell that is anode is positive in galvanic cell and negative in electrolysis cell. But the selection of electrodes is based upon the reaction that occurs, at anode oxidation takes place and at cathode reduced reaction takes place.