Question

In the electrolysis of which solution, $O{{H}^{-}}$ ions are discharged in preference to $C{{l}^{-}}$ ions?
(a) dil. NaCl
(b) Very dil. NaCl
(c) Fused NaCl
(d) Solid NaCl

Answer 1

Hint: Electrolysis is the process by which any metal can be extracted or purified, or electrical energy can be obtained. The set up for this process consists of two electrodes, anode and cathode as positive and negative electrodes. This process involves the dissociation of an electrolyte that creates ions. The ions undergo reduction and oxidation to produce products. A dilute solution means less concentration of electrolyte.

Complete answer:
Electrolysis involves an electrolyte that is taken into an aqueous salt solution. The ions of the electrolyte get dissociated in the aqueous solution. This results in oxidation or reduction reactions that create the movement of ions to get them deposited at one of the electrodes or to be released as gases.
Anode is the positive electrode on which the negative ions are attracted, while at the cathode the positive ions are attracted. The discharge or attraction of ions depends on the concentration of the aqueous solution.
Here, we have to detect the solutions that have hydroxide ions $O{{H}^{-}}$ in preference to chloride ions $C{{l}^{-}}$. This will happen when there will be very less concentration of the chloride ions and more concentration of the hydroxide ions. So, the condition applicable is the very dilute NaCl. Due to it being very dil. NaCl the reaction will be:
$2O{{H}^{-}}\to {{H}_{2}}O+\frac{1}{2}{{O}_{2}}+2{{e}^{-}}$ at the anode, while at cathode will be$2{{H}^{+}}+2{{e}^{-}}\to {{H}_{2}}$
Hence, very dil. NaCl will have $O{{H}^{-}}$ ions in preference.

So, option (b) is correct.

Note:
In this type of solution, oxygen gas will be liberated at the anode. When a concentrated NaCl solution is subjected to electrolysis then chloride ions move towards the anode that results in the liberation of chlorine gas. At the cathode there will be deposition of sodium in this type of electrolysis.