Which of the following is needed to change the state of a substance?

The correct choice is latent heat because this form of energy is specifically associated with the phase changes of a substance, such as from solid to liquid (melting) or from liquid to gas (vaporization). When a substance undergoes a change in state, heat is either absorbed or released without a change in temperature, which is precisely what latent heat refers to. For example, when ice melts into water, it absorbs heat energy from its surroundings, but its temperature does not increase until all of the ice has transitioned to water.

Specific heat pertains to the amount of energy required to raise the temperature of a substance without changing its state, which does not apply to phase changes. Conduction relates to the transfer of heat through materials, but it does not directly involve a phase change. Vaporization is a process that occurs when a substance changes from a liquid to a gas, but it's the latent heat that quantifies the energy necessary for this transition.