Answer: Option (A) is the correct answer.
Explanation:
Heat energy gained means the molecules have gained kinetic energy because kinetic energy is directly proportional to temperature.
More is the increase in temperature more will be the kinetic energy of molecules.
For example, when solid converts into liquid then it means solid substance has absorbed heat. Similarly, when liquid changes to gas or solid directly changes into gas then heat is absorbed due to which increase in kinetic energy has favored the phase change.
Thus, we can conclude that arrows 1, 2, 3 represent the phase transitions in which heat energy is gained.
