Question

when electricity is passed through water , bubbles of oxygen and hydrogen are respectively released at electrodes connected to and terminals of a cell

Answer 1

When electric current is passed through water , it decomposes to give hydrogen gas and oxygen gas.

                 ELECTRICITY
2H₂O(I) ---------------------------- > 2H₂(g) + O₂(g)

Water  splits up into H+ ions and OH- ions .
Positive H+ ions will move towards the negative terminal that is cathode and OH- ions will move towards anode.

At cathode :
H+ ions will gain electrons and form Hydrogen gas 

2H⁺ +2e--->H2 (g)

At anode : Oxygen gas will be released 

4 OH⁻(aq)→O2(g) + 2 H2O(l) + 4 e−

Answer 2

When an electric current is passed through water, “Electrolysis of water” occurs, which is the decomposition of water (H2O) into hydrogen gas (H2) and oxygen (O2).

 

The reaction ideally requires a potential difference of 1.23 volts in order for the water molecules to split up. The DC (power source of electricity) is connected to the 2 electrodes placed in water.

 

A reduction reaction occurs at the negatively charged cathode and an oxidation reaction occurs at the positively charged anode. Hydrogen gas forms at the cathode where the electrons enter the water and at the anode, oxygen is formed.

 

Cathode (reduction): 2 H2O(l) + 2e− → H2(g) + 2 OH−(aq)   Anode (oxidation): 4 OH−(aq) → O2(g) + 2 H2O(l) + 4 e−

 

By combining the pair yields of the half reaction, the overall decomposition of water into oxygen and hydrogen occurs as below:

 

Overall reaction: 2 H2O(l) → 2 H2(g) + O2(g)