Magnesium's slow reaction with cold water

Steps:

• Recall magnesium is reactive but reacts slowly with cold water due to its position in the reactivity series.
• Identify the reaction: Mg + 2H₂O → Mg(OH)₂ + H₂, producing hydrogen gas bubbles.
• Note the rate: In cold water, the reaction is sluggish, not vigorous.
• Compare to options: Slow bubble formation matches the observed gentle fizzing on the metal.

Why B is correct:

• Hydrogen gas evolves slowly from the reaction, forming bubbles directly on the magnesium surface, as per the equation Mg + 2H₂O → Mg(OH)₂ + H₂.

Why the others are wrong:

• A: Vigorous effervescence occurs with hot water or steam, not cold.
• C: Magnesium sinks in water and reacts slowly, not quickly or floating.
• D: No glowing happens; white solid (Mg(OH)₂) forms but without luminescence.

Final answer: B