Which half-reaction equation represents the
reduction of a potassium ion?
(1) k+ + e-- ==> k (3) k+ ==> k + e--
(2) k + e-- ==> k+ (4) k==> k+ + e--

Answer : The correct option is, (1)

Explanation :

Oxidation-reduction reaction : It is a type of reaction where the oxidation and reduction reaction takes place simultaneously.

Oxidation reaction : It is a reaction in which a substance looses its electrons. In this, oxidation state of an element increases. Or we can say that in oxidation, the loss of electrons takes place.

Reduction reaction : It is the reaction in which a substance gains electrons. In this, oxidation state of an element decreases. Or we can say that in reduction, the gain of electrons takes place.

As per question, the half-reaction equation of reduction of a potassium ion will be :

In this reaction, the oxidation state of potassium changes from (+1) to (0) that means the oxidation state decreases. So, this reaction shows the half-reaction equation of reduction of a potassium ion.

Therefore, the correct option is, (1)

"the periodic table is arranged in order of atomic number."