Substances are first divided into pure substances and mixtures, pure substances are divided into simple substances and compounds, compounds are divided into organic compounds and inorganic compounds, and inorganic compounds are divided into acids, bases, salts and oxides. So salt must be pure first. In the field of chemistry, salt, that is, sodium chloride, refers to pure substances. But if there is fine print in front of the salt, it is refined salt, and it must be a mixture. Because refined salt solution is not pure salt.