Which of the following elements is not diatomic in its standard elemental form?

• A. Chlorine (Cl_2)
• B. Nitrogen (N_2)
• C. Oxygen (O_2)
• D. Carbon (C)

Answer: (D)

Verified step by step guidance

1. Understand what it means for an element to be diatomic in its standard elemental form: diatomic elements naturally exist as molecules composed of two atoms bonded together, such as \(\mathrm{Cl}_2\), \(\mathrm{N}_2\), and \(\mathrm{O}_2\).
2. Recall the common diatomic elements at standard conditions (room temperature and atmospheric pressure), which are hydrogen (\(\mathrm{H}_2\)), nitrogen (\(\mathrm{N}_2\)), oxygen (\(\mathrm{O}_2\)), fluorine (\(\mathrm{F}_2\)), chlorine (\(\mathrm{Cl}_2\)), bromine (\(\mathrm{Br}_2\)), and iodine (\(\mathrm{I}_2\)).
3. Identify that carbon (C) does not naturally exist as a diatomic molecule; instead, it exists in various allotropes such as graphite, diamond, or amorphous carbon, which are composed of many atoms bonded in extended networks rather than pairs.
4. Compare the given options: chlorine (\(\mathrm{Cl}_2\)), nitrogen (\(\mathrm{N}_2\)), and oxygen (\(\mathrm{O}_2\)) are all diatomic molecules, while carbon is not diatomic in its elemental form.
5. Conclude that the element which is not diatomic in its standard elemental form is carbon (C).