* BTB is a pH indicator: BTB changes color depending on the acidity or alkalinity of a solution. It is blue in basic solutions, yellow in acidic solutions, and green in neutral solutions.

* NaCl is a neutral salt: Sodium chloride is a salt formed from a strong acid (hydrochloric acid) and a strong base (sodium hydroxide). When dissolved in water, it does not significantly alter the pH of the solution.

Therefore, adding NaCl to a solution of BTB will not cause a color change because it will not change the pH of the solution.

Important Note: While NaCl itself does not affect BTB, the presence of other substances in the solution could affect BTB's color. For example, if the solution contains a strong acid or base, the pH would change, and BTB would change color accordingly.