Final answer:
The phase of a substance (solid, liquid, gas, or plasma) is mainly determined by its temperature, which affects the balance between particle kinetic energy and intermolecular forces.
Step-by-step explanation:
The most responsible factor for whether a substance takes the phase of solid, liquid, gas, or plasma is primarily its temperature and, to a lesser extent, pressure. These factors determine the balance between the kinetic energy of the particles and the intermolecular forces (IMFs) acting between them. At low temperatures, particles have less kinetic energy and IMFs dominate, keeping the substance in a solid state. As temperature increases, the kinetic energy of the particles also increases, leading to the melting of the solid into a liquid and eventually the vaporization of the liquid into a gas. If enough heat is added, a gas can become plasma. Phase changes can also depend on changes in pressure but are predominantly influenced by temperature as described in a phase diagram.