Which color indicates a strong acid on the universal indicator scale?

The color red on the universal indicator scale signifies a strong acid. Universal indicators are designed to provide a range of colors corresponding to the pH level of a solution. A pH less than 3 typically represents strong acids, and red is the color that indicates this acidic condition.

In a universal indicator, the color shifts progressively with the pH levels: red appears for very low pH (strong acids), while higher pH levels will show different colors. For instance, green represents a neutral pH around 7, which is the normal level for pure water, and blue indicates a more basic or alkaline solution. Therefore, the appearance of red is clearly indicative of a strong acidic environment conducive to a pH value below 3.