Question

Which statement about electrolysis reaction is correct?
A. When concentrated aqueous sodium chloride is electrolysed, sodium forms at the cathode.
B. When concentrated hydrochloric acid is electrolysed, a green gas forms at the cathode.
C. When dilute sulfuric acid is electrolysed, a colourless gas forms at both electrodes.
D. When molten lead (II) bromide is electrolysed, lead forms at the anode.

Answer 1

Hint:
Take into consideration the reactions that occur at the anodes and cathodes of each electrolytic reaction. Write the half-cell reactions at each electrode and deduce the products of the reactions.

Complete step by step solution:
We can solve this problem by considering all the options one by one.
When concentrated aqueous sodium chloride is electrolysed, water can also undergo reduction and oxidation reactions at different potentials. At cathode, water can be reduced to hydrogen gas or sodium ions reduced to sodium metal. So, sodium forms at the cathode. Therefore, option ‘A. When concentrated aqueous sodium chloride is electrolysed, sodium forms at the cathode.’ is correct.
When the concentrated hydrochloric acid is electrolysed, chlorine gas is formed at the anode which results in a green colour. So, green gas is not produced in the cathode. So, option ‘B. When concentrated hydrochloric acid is electrolysed, a green gas forms at the cathode.’ is incorrect.
When dilute hydrochloric acid is electrolysed, hydrogen gas is produced at cathode and oxygen gas is produced at anode. Since both are colourless gas, option ‘C. When dilute sulfuric acid is electrolysed, a colourless gas forms at both electrodes.’ is correct.
When molten lead bromide is electrolysed, lead atoms are formed at the cathode and bromine molecules are formed at anode. So, option ‘D. When molten lead (II) bromide is electrolysed, lead forms at the anode.’ is incorrect.
Therefore, option ‘A’ and ‘C’ are correct.

Note:
Remember that the cathode is the negatively charged electrode at which the cations are attracted and then reduced. Whereas, the anode is the positive electrode at which negatively charged anions are attracted and then oxidized.