An element A reacts with water to form a solution which turms phenolphthalein solution pink. The element A is most likely to be:

Correct option is B

The correct answer is (b) Mg

Key Points:

Magnesium:

• Magnesium is a chemical element with the atomic number12and the symbol Mg.
• It is a shiny gray metal, characterized by its:
  • Low density.
  • High chemical reactivity.
  • Low melting point.
• As an alkaline earth metal in Group 2 of the periodic table, magnesium typically exhibits an oxidation state of+2.
• In nature, magnesium occurs only in combined forms due to its reactivity.
•  Magnesium reacts with water, especially at higher temperatures, to form magnesium hydroxide$$(Mg(OH)_2)$$​Which is a weak base. This base turns phenolphthalein solution pink.
  

Reaction of Magnesium with Water: 

$$Mg+2H_2O →Mg(OH)_2+H_2$$

The $$Mg(OH)_2$$ formed is slightly soluble in water, releasing enough$$\text{OH}^-$$ ions to create a basic solution, which results in the pink coloration when phenolphthalein is added.

Information booster:

​​​Phenolphthalein:

• Phenolphthalein is an indicator used to test the pH of a solution.
• It appears:
  • Colorless in acidic and neutral solutions.
  • Pink in basic solutions (pH above 8.2).
• When magnesium reacts with water, the resulting magnesium hydroxide raises the pH, causing phenolphthalein to turn pink.