Concept:Alkaline earth metals show greater reactivity with water on moving down the group.
Explanation:The elements involved are group 2 metals: beryllium (
Be), magnesium (
Mg), calcium (
Ca), and strontium (
Sr).
Reactivity increases down the group because atomic size increases, making it easier for the metal to lose its two outer electrons.
Beryllium does not react with water at all.
Magnesium reacts only with steam, not cold water.
Calcium reacts moderately with cold water.
Strontium, being lower in the group than calcium, reacts more spontaneously and vigorously with cold water.
Therefore, strontium is the most reactive among the given options.
Answer: D. Strontium