Temperature remains constant during phase transitions like melting because added heat goes into changing the state rather than increasing kinetic energy, making this a fundamental thermodynamic principle that requires no citation.
The claim that temperature remains constant during phase transitions such as melting is a basic, universally accepted physical fact governed by the principles of latent heat and thermodynamic equilibrium. It is part of foundational science education and everyday physical observation. Therefore, it is categorized as common knowledge and does not require empirical citation.