Certainly! The reaction in question is:
[tex]\[ H_2 + Cl_2 \longrightarrow 2HCl \][/tex]
This specific reaction between hydrogen gas (H_2) and chlorine gas (Cl_2) to form hydrogen chloride (HCl) doesn't proceed readily under normal conditions. It requires a specific factor to initiate the reaction.
1. Catalyst: Catalysts are substances that increase the rate of a reaction without being consumed by the reaction itself. However, in this case, the reaction between H_2 and Cl_2 does not typically require a catalyst to proceed.
2. Electricity: Electricity can be used to induce various types of chemical reactions, particularly in electrochemical cells. However, it is not the required factor for initiating the H_2 and Cl_2 reaction.
3. Heat: Heat can provide the necessary energy to overcome the activation energy barrier in some reactions, making them proceed faster. While heat can influence this reaction, it is not the specific requirement to initiate it.
4. Light: The reaction between hydrogen and chlorine to form hydrogen chloride is a photochemical reaction. This means it specifically requires light to get started. The light provides the necessary energy to break the chlorine molecules (Cl_2) into individual chlorine atoms, which then react with hydrogen molecules (H_2) to form hydrogen chloride molecules (HCl).
Given the nature of the reaction in question, the required factor is light.
Thus, the correct answer is [tex]\(\boxed{d \text{) Light}}\)[/tex].
