Methane (CH₄) is a colorless and odorless gas under standard conditions, highly insoluble in water, and non-reactive with strong oxidizing agents like potassium permanganate or with strong acids or bases. Methane is a very important fuel. It can be used as a standard fuel for water heaters and gas stoves, and for calorific value testing. It is also used as a standard gas and calibration gas for combustible gas detectors. Additionally, methane serves as a carbon source for solar cells, chemical vapor deposition of amorphous silicon films, and as a raw material in pharmaceutical and chemical synthesis. Methane is widely used in the production of ammonia, urea, and carbon black. It is used to produce methanol, hydrogen, acetylene, ethylene, formaldehyde, carbon disulfide, nitromethane, hydrogen cyanide, and butane-1,4-diol. Chlorination of methane can yield monochloromethane, dichloromethane, trichloromethane, and tetrachloromethane.