Reaction of alkaline earth metals with water produces basic solutions

Steps:

• Metals like calcium react vigorously with water, producing hydrogen gas and metal hydroxide.
• The hydroxide dissolves to form an alkaline solution.
• Litmus turns blue in alkaline (basic) conditions.
• Vigorous reaction rules out slower-reacting magnesium.

Why A is correct:

• Calcium hydroxide, Ca(OH)₂, is a base that increases pH above 7, turning litmus blue per acid-base indicator properties.

Why the others are wrong:

• B: Calcium reaction yields basic, not acidic, solution (red litmus indicates acid).
• C: Magnesium reacts too slowly with cold water for vigorous reaction; solution would be blue, not red.
• D: Same as C; incorrect color and reaction vigor.

Final answer: A