**Core Concept**
The question is testing the student's knowledge of the composition of dry air in the lower atmosphere, specifically the relative abundance of gases other than nitrogen and oxygen. The correct answer requires an understanding of the atmospheric gases and their proportions.

**Why the Correct Answer is Right**
The dry air of the lower atmosphere is primarily composed of nitrogen (78%) and oxygen (21%). The next most abundant gas is argon, which makes up approximately 0.9% of the dry air. Argon is an inert gas that is present in the atmosphere as a result of the decay of potassium-40 in the Earth's crust.

**Why Each Wrong Option is Incorrect**
* **Option A:** Carbon dioxide is a greenhouse gas and is present in the atmosphere, but it is not the next most abundant gas after nitrogen and oxygen. Its concentration has been increasing due to human activities, but it still makes up only about 0.04% of the dry air.
* **Option B:** Neon is a noble gas, but it is present in very small amounts in the atmosphere, making up only about 0.0018% of the dry air. It is not the next most abundant gas.
* **Option D:** Hydrogen is a highly reactive gas that is not present in significant amounts in the dry air of the lower atmosphere. It is often associated with water and other compounds, but as a standalone gas, it is not a major component of the atmosphere.

**Clinical Pearl / High-Yield Fact**
The atmosphere's composition plays a crucial role in supporting life on Earth. The balance of gases, including oxygen, nitrogen, and argon, is essential for human respiration and other biological processes.

**Correct Answer:** C. Argon.