Ethylene is a gas at room temperature and acts as a phytohormone.

Climacteric fruits exhibit a burst of ethylene production during their ripening phase.

Commercially, 'Ethephon' ($C_{2}H_{6}ClO_{3}P$) is often used as a source of ethylene gas.

Uniform ripening of fruit batches.

Controlled shelf-life management for commercial transport.

Safer compared to illegal chemicals like calcium carbide.

Excessive exposure can lead to over-ripening and rapid decay.

Requires controlled atmospheric chambers for optimal results.

Commercial fruit ripening chambers.

Synchronization of harvest cycles in agricultural supply chains.

Option D (Acetylene) is commonly used in the form of calcium carbide ($CaC_{2}$) for illegal ripening, but it is harmful to health due to impurities like arsenic and phosphorus.

Methane ($CH_{4}$) and Propane ($C_{3}H_{8}$) are alkanes used primarily as fuels and play no role in biological fruit ripening.