Which one of the following elements has a melting point below 0°C?

The melting point of an element is the temperature at which it changes from a solid to a liquid. This property depends largely on the strength of the forces holding its atoms or molecules together. Elements with strong bonding forces have high melting points, while those with weak forces melt at very low temperatures.

Among the elements listed — nitrogen (N), phosphorus (P), carbon (C), and bismuth (Bi) — the one with a melting point below 0°C is nitrogen.
Nitrogen exists in nature as a diatomic molecule (N₂). These molecules are bound together in the solid state by weak van der Waals forces, not by strong covalent or metallic bonds. Because of these weak intermolecular attractions, only a small amount of thermal energy is needed to separate the molecules and convert solid nitrogen into a liquid or gas.

The melting point of nitrogen is approximately −210°C, and its boiling point is around −196°C, both far below 0°C. At ordinary room temperature and pressure, nitrogen exists as a colorless and odorless gas, making up about 78% of the Earth’s atmosphere.

For comparison:

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  Phosphorus (P) exists as P₄ molecules but is solid at room temperature with a melting point around 44°C (white phosphorus).

  
  


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  Carbon (C) is a network covalent solid (graphite or diamond), having an extremely high melting point above 3500°C.

  
  


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  Bismuth (Bi) is a metallic element with a melting point near 271°C.

  
  

Therefore, among all the given elements, nitrogen (N) is the only one whose melting point lies well below 0°C due to its molecular nature and weak intermolecular forces. This property also explains why nitrogen is found as a gas under normal conditions, unlike the other elements listed