Oxidation Number And Oxidation States

Step 1: Understanding the Concept:
Oxidation state (number) is the charge an atom would have if all bonds were completely ionic.

Step 2: Detailed Explanation:
In the reaction, on the left side is in its elemental form. The oxidation state of any element in its free state is 0. In the product , Magnesium is a metal and Nitrogen is a non-metal. The compound is ionic, consisting of Mg and N ions. The oxidation state of Magnesium in is +2. Therefore, the change is from 0 to +2.

Step 3: Final Answer:
The change in oxidation state of Magnesium is from 0 to +2.

Concept: Sum of oxidation numbers = 0.

Step 1: For .

Step 1: Understanding the Concept:
The oxidation state is the hypothetical charge an atom would have if all its bonds to different atoms were fully ionic. While oxygen typically has an oxidation state of -2, peroxides are a key exception due to the presence of an oxygen-oxygen single bond ( ).
Step 2: Key Formula or Approach:
The fundamental rule for finding oxidation numbers is that the algebraic sum of the oxidation states of all atoms in a neutral molecule must equal zero. Let the oxidation state of the unknown atom be .
Step 3: Detailed Explanation:
The given compound is hydrogen peroxide, .
The generally accepted rules for assigning oxidation numbers state that:
- The oxidation state of Hydrogen (H) when bonded to non-metals is +1.
Let the oxidation state of Oxygen (O) in this compound be .
Applying the sum rule for the neutral molecule :





Therefore, each oxygen atom in has an oxidation state of -1. This is characteristic of the peroxide ion ( ).
Step 4: Final Answer:
The oxidation state of oxygen in is -1.

Step 1: Understanding the Question:
The goal is to determine the individual oxidation states of Carbon (C) and Hydrogen (H) in a neutral molecule of methane ( ).

Step 2: Key Rules or Approach:
The following standard rules for assigning oxidation states are applied:
1. The oxidation state of Hydrogen is when it is bonded to non-metals (Carbon is a non-metal).
2. For any neutral molecule, the algebraic sum of the oxidation states of all its constituent atoms must be zero.

Step 3: Detailed Explanation:
Let the unknown oxidation state of Carbon be represented as .
Methane ( ) consists of one Carbon atom and four Hydrogen atoms.
As per the rules, each Hydrogen atom is assigned an oxidation state of .
Applying the rule for the sum of oxidation states in a neutral molecule:

Substituting the assigned value for Hydrogen:



This calculation confirms that Carbon has an oxidation state of and each Hydrogen atom has an oxidation state of .

Step 4: Final Answer:
The oxidation states of C and H in are and respectively, which corresponds to option (B).

Step 1: Understanding the Concept:
Potassium (K) is an alkali metal belonging to Group 1 of the periodic table. Alkali metals have a single valence electron in their outermost shell, which they lose very easily to achieve a stable noble gas configuration.

Step 2: Detailed Explanation:
1. Alkali metals, including potassium, always exhibit an oxidation state of in their compounds.
2. In (Potassium oxide), oxygen is in the state. Calculation: .
3. In (Potassium peroxide), oxygen is in the state (peroxide ion ). Calculation: .
4. In (Potassium superoxide), oxygen is in the state (superoxide ion ). Calculation: .

Step 3: Final Answer
The oxidation number of potassium remains in all three compounds.