An element Z reacts with water to form a solution which turns phenolphthalein indicator pink. The element X is most likely to be:

Phenolphthalein is an indicator used in acid-base titrations. It turns colorless in acidic solutions and pink in basic solutions. Sodium is a metal which reacts with water to form sodium hydroxide, which is a base. Hence, phenolphthalein turns the solution pink.

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