consider the following reaction equation: 2NH$_3$ .+ 3Cl$_2$ → N2 + 6HCl.  NH$_3$ is acting as?

Analyze the question: We need to decide what role NH₃ plays in the reaction 2NH₃ + 3Cl₂ → N₂ + 6HCl. To do this, we track oxidation numbers.

Concept:

• A reducing agent gets oxidized (loses electrons, so its oxidation number increases).
• An oxidizing agent gets reduced (gains electrons, so its oxidation number decreases).
• Dehydrating and drying agents remove water, which is not relevant here.

Step-by-step solution:

1. Oxidation number of N in NH₃: N + 3(+1) = 0, so N = -3

2. Oxidation number of N in N₂ (free element): 0

Nitrogen goes from -3 to 0. Its oxidation number increases, so nitrogen is oxidized.

3. Oxidation number of Cl in Cl₂: 0. In HCl: -1. Chlorine goes from 0 to -1, so it is reduced. This makes Cl₂ the oxidizing agent.

4. Since NH₃ is oxidized, it donates electrons to chlorine, so NH₃ is the reducing agent.

Answer: Option A, a reducing agent.

Tip: Use "OIL RIG": Oxidation Is Loss (of electrons), Reduction Is Gain. The substance that is oxidized is always the reducing agent. In redox questions, quickly assign oxidation numbers to the element that changes, and the role becomes clear.