Let's analyze both statements given to determine the correct answer.

Statement (I) describes a buffer solution as a mixture of a salt and an acid or a base mixed in any particular quantities. However, this definition is partially incorrect. A buffer solution is more accurately defined as a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. The purpose of a buffer solution is to maintain a stable pH when small amounts of acid (H⁺ ions) or alkali (OH⁻ ions) are added. It is not just any mixture of a salt and an acid or base but must involve components that can react with added acid or base to minimize changes in pH.

Therefore, Statement (I) is misleading or incomplete as it omits the necessity for a weak acid and its conjugate base or a weak base and its conjugate acid to form a true buffer solution.

Statement (II) mentions that blood is a naturally occurring buffer solution whose pH is maintained by the $$\mathrm{H}_2\mathrm{CO}_3/\mathrm{HCO}_3^{-}$$ (carbonic acid/bicarbonate) system. This is accurate. The carbonic acid-bicarbonate buffering system is one of the main buffering systems in human blood, helping to maintain the pH within a narrow range (typically around 7.35 to 7.45). This buffer system works by the reversible reaction between carbon dioxide (CO₂) and water to form carbonic acid ($$\mathrm{H}_2\mathrm{CO}_3$$), which can then dissociate into bicarbonate ion ($$\mathrm{HCO}_3^{-}$$) and a hydrogen ion (H⁺). This system effectively moderates changes in pH by either consuming or releasing H⁺ ions.

Given this analysis:

Statement I is false because it inaccurately or incompletely describes a buffer solution.

Statement II is true as it correctly identifies blood as a naturally occurring buffer solution that uses the $$\mathrm{H}_2\mathrm{CO}_3/\mathrm{HCO}_3^{-}$$ system to maintain pH.

Therefore, the correct answer is:

Option C: Statement I is false but Statement II is true.