Question

Name the gas released at the cathode when acidulated water is electrolyzed.
(A) Hydrogen
(B) Nitrogen
(C) Oxygen
(D) None of the above

Answer 1

Here, you are given three gases as options and are asked to find the gas which will release at cathode when acidulated water is electrolyzed and if some other gas is released, option (D) is there in that case. Now, in order to answer this question, you need to first consider the event that happens at the cathode and also give a thought on what electrolysis is. After having all these things in your mind, you can carry out the appropriate reactions that will be occurring during the electrolysis and look for the gas that will form at the cathode. Also, do not forget the term acidulated used in the question.

Complete step by step solution:
First of all, let us have a look at electrolysis. Electrolysis is a process in which direct electric current is passed in an electrolyte which leads to chemical reactions at the electrodes. These electrodes are cathode and anode. They are immersed in solutions separate from each other and are connected to a power source and then a current flows as the circuit is complete.
Cathode are electrodes where the process of reduction happens, basically it is an electron acceptor. Now, we will look at the reactions that occur when acidulated water is electrolyzed.
At anode: $2{H_2}O \to {O_2} + 4{H^ + } + 4{e^ - }$
At cathode: $4{H_2}O + 4{e^ - } \to 2{H_2} + 4O{H^ - }$
As you can see that the gas released in the above equation at the cathode is ${H_2}$, that is hydrogen gas.
Therefore, the gas released at the cathode when acidulated water is electrolyzed is Hydrogen.
Option (A) is correct.

Note :
Here, we have discussed in brief about electrolysis. You should keep in mind that the cathode is electron acceptor whereas anode is electron donor, in other words, reduction happens at cathode and oxidation happens at anode. In order to remember this, you can memorize it as ‘red cat’ and ‘an ox’. Also remember the reactions at cathode and anode which took place while the electrolysis of acidulated water.