Final answer:
Absolute zero is the temperature at which all molecular motion ceases, defined as 0 Kelvin. It is a theoretical limit that has never been fully reached but approximated in laboratory conditions. The temperature of a substance at this point is directly proportional to the average kinetic energy of its particles, which would be zero at absolute zero.
Step-by-step explanation:
The temperature at which all molecular motion stops is known as absolute zero. Absolute zero is theoretically the lowest possible temperature where the internal energy of a system is minimal due to the cessation of molecular motion. This temperature is defined as 0 Kelvin (K), which is equivalent to -273.15°C or -459.67°F. In the Kelvin scale, which is based on molecular motion, the temperature of a substance is directly proportional to the average kinetic energy of its particles. While absolute zero has never been achieved in practice, scientists have managed to reach temperatures extremely close to this theoretical limit in laboratory settings.
It is important to correct the inaccurate statement (c) that the speed of particles increases to a maximum at absolute zero. In fact, it is point (d) which correctly states that the internal energy approaches zero because the speed of particles decreases to zero at this temperature.