Sodium and chlorine are indeed poisonous in their elemental forms. However, when combined, they form sodium chloride, commonly known as table salt, which is a safe and essential nutrient for human life.

Here's why:

* Chemical Reaction: When sodium (Na) and chlorine (Cl) react, they undergo a chemical reaction to form sodium chloride (NaCl). This reaction creates a completely new substance with different properties than its individual components.

* Ionic Bonding: Sodium chloride is an ionic compound, meaning it's formed by the attraction between positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-). These ions are held together by electrostatic forces, creating a stable, non-toxic compound.

* Essential Nutrient: Sodium chloride is crucial for maintaining proper fluid balance, nerve function, and muscle contraction in the body. It's a vital electrolyte and plays a role in many physiological processes.

Therefore, while sodium and chlorine are dangerous in their pure forms, the chemical transformation into sodium chloride renders them safe and beneficial for consumption.