Question

Which is the strongest oxidising agent out of the following?
A ) \[{{\text{I}}_2}\]
B ) \[{\text{C}}{{\text{l}}_2}\]
C ) \[{\text{B}}{{\text{r}}_2}\]
D ) \[{{\text{F}}_2}\]

Answer 1

Hint: Halogens (fluorine, chlorine, bromine and iodine) have strong oxidising power due to high electronegativity values. They readily accept an electron. Gain of electrons is reduction. Thus, halogens are easily reduced. A substance that itself is reduced acts as an oxidising agent. In the presence of a halogen atom, the atom of another element easily loses electrons to complete its octet. Loss of electrons is oxidation. Thus, in the presence of halogen, other atoms are oxidised. So halogen is an oxidising agent.

Complete step by step answer:
The general electronic configuration of halogens is \[n{s^2}n{p^5}\]. Highly electronegative halogen atoms have seven valence electrons and can easily accept an electron to complete octet and attain stability.
Consider the factors affecting the oxidizing tendency. These factors include bond dissociation enthalpy, electron gain enthalpy and hydration enthalpy. With increase in the electronegativity, the oxidising power of halogen increases. Among halogens, fluorine is the most electronegative element. On the pauling scale, the electronegativity value of fluorine is 3.98. Hence, among halogens, fluorine has highest electronegativity.
Among halogens, the electron gain enthalpy increases with increase in atomic size.
As you know that fluorine has small size, so you also know that fluorine has lower electron gain enthalpy than chlorine. But fluorine has low bond dissociation enthalpy and high hydration enthalpy than chlorine. Low bond dissociation enthalpy and high hydration enthalpy of fluorine (as compared to corresponding values of chlorine) compensate for lower electron gain enthalpy. Thus, despite having lower electron gain enthalpy, fluorine is the strongest oxidizing agent than chlorine as it has low bond dissociation enthalpy and high hydration enthalpy than chlorine.

Hence, write the option D ) \[{{\text{F}}_2}\] as the correct answer.

Additional Information: Fluorine can oxidize chloride, bromide and iodide ions in solution or in solid phase. Chlorine can only oxidise bromide or iodide ion. Bromine can oxidise only iodide ion.

Note: Do not consider only electron gain enthalpy. Fluorine has low electron gain enthalpy than chlorine. However fluorine is a better oxidising agent than chlorine. To account for this, additional factors such as low bond dissociation enthalpy and high hydration enthalpy for fluorine should be considered.