With respect to the constituents causing alkalinity in water, which of the following situation never arises?

To understand the constituents causing alkalinity in water, we need to look at the factors that contribute to it. Alkalinity in water primarily results from the presence of bases, particularly carbonate (CO₃²⁻), bicarbonate (HCO₃⁻), and hydroxide ions (OH⁻).

In situations involving water chemistry, certain conditions will not contribute to alkalinity:

1. Pure Water: A pure water sample without any dissolved salts or minerals will not have any alkalinity because it lacks the necessary ions (like carbonate or hydroxide) to provide a basic environment.

2. Strong Acidic Solutions: If water is contaminated or mixed with strong acids (like HCl or sulfuric acid), the alkalinity will decrease significantly, potentially to zero, because the concentration of hydrogen ions (H⁺) will dominate, balancing or exceeding the basic ions present.

Based on the above analysis, any scenario that involves pure water devoid of dissolved alkaline substances or the introduction of strong acids would not contribute to alkalinity in water. Therefore, the situation where pure water or a strongly acidic solution arises will never lead to alkalinity.