Which of the following statements about latent heat for a given substance is/are correct ? 1. It is fixed at a given temperature. 2. It depends upon the temperature and volume. 3. It is independent of temperature and volume. 4. It depends on the temperature but independent of volume. Select the correct answer using the code given below :

Latent heat is the energy absorbed or released during a phase change at a constant temperature [1]. For a given substance, the latent heat is fixed at a specific temperature [1]. However, it is not a universal constant; it varies with the temperature at which the phase transition occurs [2]. For instance, the latent heat of vaporization for water decreases as temperature increases. According to the Clausius-Clapeyron relation, in a univariant system where two phases coexist, pressure and temperature are dependent on each other [2]. Consequently, while latent heat depends on temperature (and by extension, the saturation pressure), it is independent of the volume of the substance. Therefore, statement 1 is correct because for a specific temperature, the value is fixed, and statement 4 is correct because it acknowledges the temperature dependence while noting volume independence.

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 22: Vertical Distribution of Temperature > Latent Heat > p. 294
2. [2] https://home.iitk.ac.in/~suller/lectures/lec28.htm