Question

Electrolysis of aqueous sodium chloride solution will form ______ at the cathode.

A. Hydrogen gas 

B. Sodium metal

C. Water

D. Chlorine gas

Answer 1

Hint: In any chemical reaction anode is the electrode where oxidation occurs and cathode is the electrode where reduction occurs. Oxidation is loss of electrons (oxidation was originally used to describe reaction in which an element combines with oxygen) and reduction is gain of electrons.

Complete step by step solution:

Electrolysis is a chemical process of decomposition produced by passing an electric current through liquid or solution containing ions.

When sodium chloride is dissolved in water it dissociates into ions. But in ionic solution water itself also undergo oxidation and reduction, so the substance which will be oxidized or reduced will not contain only sodium chloride ion but may also include water ion

At anode

$2{H_2}O(l) + 2{e^ - }\xrightarrow{{}}{H_2}(g) + 2O{H^ - }$ 

$N{a^ + }(l) + {e^ - }\xrightarrow{{}}Na(l)$ 

At cathode

$2{H_2}O(l)\xrightarrow{{}}{O_2}(g) + 4{H^ + } + 4{e^ - }$ 

$2C{l^ - }\xrightarrow{{}}C{l_2}(g) + 2{e^ - }$ 

So we can see 

At anode sodium metal and hydrogen gas are liberated.

At cathode oxygen gas and chlorine gas are liberated. In options chlorine gas is given, so, answer to this question is option D that is chlorine gas.

Additional information: 

1. Sodium chloride solution is also called Brine. Electrolysis of brine is a large-scale process used to manufacture chlorine from salt. Other useful products of this reaction are sodium hydroxide $NaOH$ and hydrogen ${H_2}$.

2. Environmental impacts of large scale electrolysis of brine- This process uses a lot of electricity that is mainly obtained by burning of fossil fuels. In this process metal must be in contact with brine. Metal commonly used is mercury, which can escape into the environment which will be harmful.

3. Uses of products obtained from electrolysis- Chlorine is used as a disinfectant and purifier. It is also used in the manufacture of hydrochloric acid and plastics.

4. Sodium hydroxide is used in processing of food products, manufacture of paper and removing pollutants from water.

5. Hydrogen is used as pollution-free fuel and is used in the manufacture of hydrochloric acid.

Note: In electrolysis of aqueous solution water also participates in oxidation and reduction reactions. Therefore you may have more than one ion arriving at each electrode and there can be a choice over which ion gets discharged.