Are all acid have covalent structure in solid state?
You are aware of the fact that there are no things like "purely covalent" and "purely ionic"?
I think there are purely covalent bonds (like between identical atoms. Between oxygen atoms in O2?).
Anyway, when not dissolved in water, I think acids would have covalent bonds between atoms in the compound and intermolecular forces (dipole-dipole interaction, hydrogen bonding, etc.) between molecules.
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