Question

Which equation describes a reduction?

Mg(s)—Mg2+ (aq) + 2e -
201 + 2e ->201
Na(s) — Nat(aq) + e
Al(s)— A3+ (aq) + 3e -

Answer 1

1,3,4 equations represent oxidation as charge increases

Your 2 nd option represents reduction

Answer 2

Answer : The reduction will be
`X_2+2e^-\rightarrow 2X^-`

Explanation :

Redox reaction or Oxidation-reduction reaction : It is defined as the reaction in which the oxidation and reduction reaction takes place simultaneously.

Oxidation reaction : It is defined as the 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 defined as 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.

(a) The given half reactions is:

`Mg(s)\rightarrow Mg^(2+)(aq)+2e^-`

This reaction is an oxidation reaction because in this reaction, the loss of electrons takes place.

(b) The given half reactions is:

`X_2+2e^-\rightarrow 2X^-`

This reaction is an reduction reaction because in this reaction, the gain of electrons takes place.

(c) The given half reactions is:

`Na(s)\rightarrow Na^(+)(aq)+e^-`

This reaction is an oxidation reaction because in this reaction, the loss of electrons takes place.

(d) The given half reactions is:

`Al(s)\rightarrow Al^(3+)(aq)+3e^-`

This reaction is an oxidation reaction because in this reaction, the loss of electrons takes place.

Hence, the reduction will be
`X_2+2e^-\rightarrow 2X^-`