Explanation:

- The Earth's atmosphere is composed predominantly of gases, with different gases present in varying proportions.

- Oxygen is the second most abundant gas in the Earth's atmosphere. It makes up about 21% of the atmosphere.

- Hydrogen is not abundant in Earth's atmosphere; it's present in trace amounts.

- Nitrogen is the most abundant gas in Earth's atmosphere, making up about 78%.

- Carbon dioxide is a trace gas, constituting approximately 0.04% of the Earth's atmosphere.

Given this information:

Option 1, Oxygen - Oxygen is indeed the second most abundant gas in the Earth's atmosphere.