Redox Reactions

The production of nascent hydrogen occurs when a metal reacts with an acid or an alkali and forms hydrogen gas. In an alkaline medium, nascent hydrogen is produced by the reaction of certain metals with hydroxide ions.

Among the given metal pairs:
1. Zn and Al: Both zinc (Zn) and aluminum (Al) can react with alkaline solutions to produce nascent hydrogen. Zinc reacts with alkalis to form hydrogen gas, and aluminum can react with alkali (especially when heated or in excess) to produce nascent hydrogen as well.
2. Fe and Ni: Both iron (Fe) and nickel (Ni) are less reactive in producing nascent hydrogen in alkaline media compared to the metals in other pairs.
3. Al and Mg: Magnesium (Mg) also reacts with alkalis to produce nascent hydrogen, but aluminum (Al) is more commonly known to produce nascent hydrogen when reacting with alkalis.
4. Mg and Zn: Magnesium reacts with alkaline solutions to form nascent hydrogen, but zinc is also quite reactive in alkaline solutions, although Al and Zn are more significant producers.

Answer: Zn and Al

(a) KIO₃ acts as an oxidizing agent in the given redox reaction.

(b) The oxidation number of iodine changes from +5 (in KIO₃) to −1 (in KI).

To determine the oxidation number of iodine:

• In KIO₃: K = +1, O = −2
  →
• In KI: K = +1, so I must be −1

Change in oxidation number: +5 → −1
That is a change of 6 units: (+4, +3, +2, +1, 0, −1)

Therefore, the equivalent mass of KIO₃ is given by:

So, the correct option is (C):

The reaction involves:

Here, each molecule of donates 1 electron, leading to a total of 2 electrons being transferred per molecule of .

Oxidation states of sulfur: In , the average oxidation state of sulfur is +2. During the reaction, sulfur in is partially oxidized to , where the average oxidation state becomes +2.5.

Definition of equivalent weight: The equivalent weight of a substance is given by: Here, represents the number of electrons transferred per molecule in the reaction.

Calculation: For , , because each molecule transfers 1 electron. Therefore, the equivalent weight of is equal to its molecular weight, . Thus, the equivalent weight of in this reaction is .