[Fish200398]

Which one from C N O P has no allotropes?

It seems to me all of them have allotropes

[chenbeier]

What is in your opinion the allotrop of nitrogen, if you would be right.
What are the allotrops of the other Elements?

[Fish200398]

The element that does NOT exhibit allotropy is bismuth. Nitrogen (solid) has two allotropes. Antimony has three allotropes. Phosphorus and arsenic has several allotropes.
(Toppr.com)

[AWK]

It all depends on the point of view and definition. The definition of Berzelius from 1841 changed many times (Berzelius considered yellow and red HgI2 to be allotropes, he knew both varieties of sulfur and from this knowledge, he proposed a definition). If only different combinations of element atoms are considered to be allotropic forms, e.g. rhombic and monoclinic sulfur is not allotropic forms, but only polymorphic forms (currently polymorphic elements are also considered as allotropic forms). The same applies to solid nitrogen - it has more than 2 polymorphic variants, i.e. more than two allotropic variants.
https://wiki2.org/en/Solid_nitrogen
  At some level of learning chemistry, low-temperature, high-temperature, and high-pressure variations are omitted if they are not present under normal conditions and then nitrogen is not allotropic.
https://periodictable.com/Properties/A/AllotropeNames.html

[Enthalpy]

More and more elements have allotropes discovered or produced. Metallic hydrogen didn't exist decades ago. Presently, researchers try to produce N₈ to serve as an explosive, that would be one allotropic form more. Ozone exists as a solid too.