Quarks, like other elementary particles, exhibit both particle-like and wave-like properties. This behavior is described by quantum mechanics, which is the theory that governs the behavior of particles at the microscopic scale.
In quantum mechanics, particles are described by wavefunctions, which are mathematical descriptions that represent the probability distribution of finding a particle in different states or locations. The wavefunction of a particle can exhibit wave-like properties, such as interference and superposition, which are characteristic of waves.
However, when a measurement is made on a particle, its wavefunction "collapses" to a specific state or location, and the particle behaves like a localized particle at that moment. This behavior is often referred to as the wave-particle duality of quantum mechanics.
In the case of quarks in your chair, they are part of the atomic nuclei that make up the atoms in the chair. Quarks are confined within these atomic nuclei and are not observed as individual free particles in everyday macroscopic objects. The behavior of quarks within the atomic nucleus is described by quantum chromodynamics (QCD), the theory of the strong interaction.
So, while quarks can exhibit wave-like properties described by their wavefunctions, within the context of the chair, they are primarily treated as particles confined within the atomic nuclei. It is the collective behavior of these particles that gives rise to the macroscopic properties of the chair that we observe in our everyday experience.