Reduction potential of fe is more than that of cr, so fe will reduce and act as cathode and cr will act as anode. now emf of cell is reduction potential of cathode - reduction potential of anode. so EMF= -0.45-(-0.75) = 0.3 V

Oxidation half reaction for a reaction is that reaction which gives us the reactant and product formed after the oxidation of the reactant. In this case Fe⁺² oxidizes itself to Fe⁺³ and so the oxidation of Fe⁺² is oxidation half reaction. Option d correct.

In the given reaction 2Ag + 2H₂​SO₄​ → Ag₂​SO4​ + H_2​O + SO₂​, sulfuric acid (H₂​SO₄​) is acting as a dehydrating agent. It removes water (dehydration) from the reactants to form products. The reaction results in the formation of silver sulfate (Ag₂​SO₄​), water (H₂​O), and sulfur dioxide (SO₂​).

The correct answer is (c) loss of electrons. In a reduction reaction, a substance gains electrons, leading to a decrease in its oxidation number and often a decrease in valency. Therefore, options (a), (b), and (d) are characteristics of reduction. The process of reduction involves the addition of electrons or a decrease in oxidation number.

Let's analyze the given reaction: 4Fe + 3O₂ → 4Fe³⁺ + 6O^2–

This is a redox reaction because both oxidation and reduction are occurring.

Now, let's evaluate the statements:

a) It is a redox reaction - Correct, as mentioned above.

b) Metallic iron is a reducing agent - Correct. In the reaction, metallic iron (4Fe4Fe) is undergoing oxidation, which means it is losing electrons and, therefore, acting as a reducing agent.

c) Fe³⁺ is an oxidizing agent - Correct. In the reaction, Fe³⁺ is gaining electrons and undergoing reduction, so it is acting as an oxidizing agent.

d) Metallic iron is reduced to Fe²⁺ - This statement is incorrect. In the given reaction, metallic iron (4Fe) is oxidized to 4Fe³⁺, not Fe²⁺.

Therefore, the correct answer is (d) Metallic iron is reduced to Fe²⁺.

The octet rule states that atoms tend to gain, lose, or share electrons in order to achieve a full set of eight electrons in their outermost electron shell (or two electrons for hydrogen). Let's examine the given molecules:

(a) NH₃ - Nitrogen has three bonds and a lone pair, which totals to 8 electrons in its valence shell. The octet rule is followed.

(b) CH₄ - Carbon forms four single bonds, completing its octet. The octet rule is followed.

(c) CO₂ - Carbon forms two double bonds with oxygen, and each oxygen has two lone pairs. Carbon and each oxygen in CO₂ have a full octet. The octet rule is followed.

(d) NO - Nitrogen forms a single bond with oxygen and has two lone pairs. Nitrogen in NO has only 6 electrons in its valence shell, violating the octet rule.

Therefore, the molecule in which the octet rule is not followed is (d) NO.

Boron in BCl₃ has 6 electrons in outermost shell. Hence BCl₃ is a electron deficient compound.