The percentage of nitrogen in air is about ______ by volume.

78%

The correct answer is Option (2) → 78%

The air we breathe is primarily composed of nitrogen (about 78% by volume), oxygen (about 21%), and small amounts of other gases like argon, carbon dioxide, and trace gases. This composition is relatively constant in Earth's atmosphere up to an altitude of about 80 kilometers. Nitrogen is essential for life and plays a crucial role in various biological and environmental processes.