窒素

1. Origins, structure, and basic meaning

• Structure: 窒素（ちっそ） is the element name nitrogen. Its reading includes a small っ in the middle.
• Basic usage: It appears in descriptions of air composition and of materials used in experiments.

2. Common pitfalls and similar expressions

• Consonant length in the reading
  • In ちっそ, the small っ lengthens the consonant at the start of そ. The distinction is made through consonant length, without inserting a separate つ syllable.
• Material and physical state
  • In 液体窒素, 液体 specifies the liquid state and 窒素 names the material. 酸素 in the first example names a different component of air.