pH scale indicates the acidity and alkalinity of a solution. pH is used to show if the solution is acidic or basic and reflects the concentration of H+ ion. pH scale values lie between 0 and 14. pH<7 means acidic solution and pH>7 reflects basic solution. HCl is an acid. As a result, it is added to the PBS solution to lower pH. Adding HCl decreases pH increasing the concentration of H+ ions and neutralising OH- ions. Therefore, the pH of 10x PBS before its adjusting was higher greater than 7.4.