Question

Which among the following statements is incorrect for magnesium metal?

• A. It burns in oxygen with a dazzling white flame.
• B. It reacts with cold water to form magnesium oxide and evolves hydrogen gas.
• C. It reacts with hot water to form magnesium hydroxide and evolves hydrogen gas.
• D. It reacts with steam to form magnesium hydroxide and evolves hydrogen gas.

Answer 1

The correct option is B

It reacts with cold water to form magnesium oxide and evolves hydrogen gas.

Explanation for correct option

(B)It reacts with cold water to form magnesium oxide and evolves hydrogen gas.

The magnesium metal does not react with cold water.

$\mathrm{Mg}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{No}\mathrm{reaction}$

Instead, the metal reacts with hot water or steam. The magnesium metal on reaction with steam liberates ${\mathrm{H}}_2$ and forms magnesium oxide.

$\mathrm{Mg}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\stackrel{100°\mathrm{C}}{\to }\mathrm{MgO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$

Explanation for incorrect options:

Option (A):

Magnesium burns with oxygen and forms a white powder of magnesium oxide. This is a combination reaction that requires some energy.

$2\mathrm{Mg}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2\mathrm{MgO}\left(\mathrm{s}\right)+\mathrm{energy}$

Option (C):

On reaction with hot water or steam, magnesium oxide is formed as a result of decomposition. Also, hydrogen gas is liberated.

$\mathrm{Mg}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\stackrel{100°\mathrm{C}}{\to }\mathrm{MgO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$

Option (D):

Magnesium forms magnesium oxide and water when it combines with steam.

$\mathrm{Mg}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\stackrel{100°\mathrm{C}}{\to }\mathrm{MgO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$

Final answer: Magnesium does not react with cold water. The statement in option B is incorrect.