The reaction of calcium carbide with water is used to generate acetylene: CaC₂ + 2H2O → H–CC–H + Ca(OH)₂. Calcium carbide, CaC2, contains the carbide ion, C²⁻₂ . Sketch the molecular orbital energy level diagram for the ion. How many π and bonds does the ion have? What is the carbon–carbon bond order? How has the bond order changed on adding electrons to C₂ to obtain C²⁻₂  ? Is the C²⁻₂  ion paramagnetic?

Acetylene is used by miners to form a bright flame in headlamps.