Arsenic (As) is a chemical element with atomic number 33. The only stable arsenic isotope is ⁷⁵As, with 33 protons and 42 neutrons.

Arsenic is a toxic element, and arsenic poisoning can be lethal. While arsenic poisoning can cause cancer, the compound Arsenic trioxide (As₂O₃) is sometimes used to treat cancer.

When alloyed with certain metals such as lead or gallium, arsenic also has some industrial uses.

Arsenic can be spelled using chemical element symbols: Ar - Se - Ni - C.