Introduction
According to the Fermi-Dirac statistic, which is one of the fundamental principles in quantum mechanics, the number of particles in a phase cell is generally limited to a value of 1. This principle is derived from the Pauli exclusion principle, which states that no two identical fermions can occupy the same quantum state simultaneously.

Explanation
The Fermi-Dirac statistic describes the statistical behavior of a large number of identical fermions, which include particles such as electrons, protons, and neutrons. Fermions are characterized by having half-integer values of spin, and they obey the Pauli exclusion principle.

Pauli Exclusion Principle
The Pauli exclusion principle states that no two identical fermions can occupy the same quantum state simultaneously. This means that if a quantum state is already occupied by a fermion, another fermion cannot occupy the same state. This exclusion principle is a consequence of the wave nature of matter and is a fundamental principle in quantum mechanics.

Phase Space and Phase Cells
In quantum mechanics, the phase space is the space of all possible states that a particle can occupy. The phase space is divided into small regions called phase cells, which represent the smallest possible regions in which a particle can be localized. Each phase cell can accommodate only one particle due to the Pauli exclusion principle.

Fermi-Dirac Distribution
The Fermi-Dirac distribution describes the statistical distribution of fermions in a system at thermal equilibrium. It gives the probability of finding a fermion in a specific energy state at a given temperature. According to this distribution, the probability of occupation of each energy state is limited to either 0 or 1, meaning that each energy state can be occupied by at most one fermion.

Conclusion
In summary, according to the Fermi-Dirac statistic, the number of particles in a phase cell is limited to 1 due to the Pauli exclusion principle. This principle ensures that no two identical fermions can occupy the same quantum state simultaneously. The Fermi-Dirac distribution describes the statistical behavior of fermions and assigns a probability of occupation to each energy state, with a maximum of 1 particle per state. This principle is fundamental in understanding the behavior of fermions and plays a crucial role in various areas of physics, such as solid-state physics and quantum mechanics.