In electrochemistry, the passage of an electric current through a conducting liquid (an electrolyte solution or molten salt) generally produces what kind of effect in the liquid?

Introduction / Context:
This general chemistry question is about what happens when an electric current passes through a conducting liquid, such as an aqueous electrolyte or a molten salt. The concept belongs to electrochemistry and is closely related to electrolysis, electroplating and the production of elements like chlorine, sodium and aluminium. Understanding that the current does not merely heat the liquid but can cause definite chemical changes is essential for many practical and industrial applications.

Given Data / Assumptions:

• A conducting liquid is present. This can be an aqueous solution of an electrolyte or a molten ionic compound.
• An electric current is passed through this conducting liquid between suitable electrodes.
• We are asked about the overall effect produced inside the liquid.
• We assume normal laboratory or industrial conditions where significant current is passed for some time.

Concept / Approach:
When an electric current passes through a conducting liquid containing ions, the positive and negative ions move towards the oppositely charged electrodes. At these electrodes, the ions can gain or lose electrons. This gain or loss of electrons is a redox (reduction–oxidation) process and leads to the formation of new substances, such as gases or deposited metals. This process is called electrolysis. Therefore, the effect of the current is not limited to physical heating or movement, but a true chemical reaction in the electrolyte and at the electrodes.

Step-by-Step Solution:
1) Identify the nature of a conducting liquid: it contains free ions (cations and anions) that can move under the influence of an electric field.2) When a potential difference is applied, cations move towards the cathode and anions move towards the anode.3) At the cathode, cations can gain electrons (reduction), forming neutral atoms or molecules, such as metal deposits or hydrogen gas.4) At the anode, anions can lose electrons (oxidation), producing neutral atoms or molecules, for example chlorine gas from chloride ions.5) These oxidation and reduction processes change the chemical composition of the solution or molten salt.6) Because new substances are formed and the original ions are consumed or transformed, the overall effect is a chemical reaction, specifically electrolysis.

Verification / Alternative check:
Consider the electrolysis of molten sodium chloride. When current passes, sodium ions are reduced at the cathode to form liquid sodium metal, and chloride ions are oxidised at the anode to form chlorine gas. Both products are chemically different from the starting ionic compound. In the electrolysis of aqueous copper sulphate with copper electrodes, copper is deposited at the cathode and dissolves from the anode. These examples clearly show that electric current through a conducting liquid leads to chemical transformations rather than mere physical changes such as warming or simple mixing.

Why Other Options Are Wrong:
Evaporation of the liquid only: Some heating may occur, but evaporation is not the main or defining effect of current in an electrolyte.
Galvanisation of the container metal: Galvanisation refers to coating iron or steel with zinc, which is a different process and not the general effect of current in any conducting liquid.
Mainly a physical change without any reaction: The movement of ions leads directly to redox reactions and formation of new substances, which is chemical, not purely physical.
Only heating of the liquid with no change in composition: Joule heating may occur, but electrolysis clearly changes composition, so this description is incomplete and misleading.

Common Pitfalls:
A frequent mistake is to think of current in liquids as similar to current in metallic wires, where the conductor itself does not change chemically. In electrolytes, however, the charge carriers are ions, and their discharge at electrodes produces new substances. Another confusion is between simple heating of the solution and electrolysis; while the solution may warm up, the hallmark of electrolysis is the appearance of gases, metal deposits or other products at the electrodes. Remember that whenever ions are discharged at electrodes, a chemical reaction has taken place.

Final Answer:
The passage of an electric current through a conducting liquid primarily causes a chemical reaction in the electrolyte (electrolysis).