The correct answer is option 3, FecIs. To determine the pH of a solution, we need to consider the concentration of hydrogen ions (H+). A pH less than 7 indicates that the solution is acidic, meaning it has a higher concentration of H+ ions.

Option 1, NaOH, is sodium hydroxide, which is a strong base. When it dissolves in water, it dissociates into sodium ions (Na+) and hydroxide ions (OH-). The presence of hydroxide ions makes the solution basic, resulting in a pH greater than 7.

Option 2, KCI, is potassium chloride, which is formed by the combination of a strong acid (hydrochloric acid) and a strong base (potassium hydroxide). The resulting solution has an overall neutral pH of 7.

Option 4, NaCI, is sodium chloride, which also forms a neutral solution with a pH of 7.

Option 3, FecIs, is ferrous chloride. When dissolved in water, it releases ferrous ions (Fe2+) and chloride ions (Cl-). The presence of ferrous ions can make the solution acidic, resulting in a pH less than 7.

Therefore, the correct