Question

When a magnesium ribbon is burned it produces.
A) Magnesium hydroxide.
B) Magnesium Oxide.
C) Magnesium chloride.
D) Magnesium sulfate.

Answer 1

We know magnesium ribbon is a type of magnesium which reacts vigorously with water so the reaction of magnesium ribbon with water is avoidable. Burning of magnesium ribbon in presence of air is an exothermic reaction.

Complete step by step answer:

We all know that magnesium is metal with atomic number $12$ and it is an element belonging to group 2 of periodic table. Magnesium rapidly reacts with air in its metal form. So, when the magnesium metal burns it reacts with oxygen present in the air. Thus after burning it forms white powdery compound named magnesium oxide during this reaction and energy is released thus it is an exothermic reaction.
The chemical reaction is written as,
$2Mg\left( g \right) + {O_2} \to 2MgO\left( s \right) + energy$
Therefore, the option B is correct.
Magnesium is additionally capable of reducing water to the highly-flammable hydrogen gas, which can be ignited by the surplus heat given by the reduction reaction.
$Mg\left( s \right) + 2{H_2}O \to Mg{\left( {OH} \right)_2}\left( s \right) + {H_2}\left( g \right)$
Magnesium reacts with water to form magnesium hydroxide. Therefore, the option A is incorrect.
Magnesium sulfate is obtained directly from dry lake beds and other natural sources. It also can be prepared by reacting magnesium carbonate and magnesium oxide with sulfuric acid. Therefore, the option D is incorrect.
Magnesium chloride is prepared by reacting magnesium hydroxide with hydrochloric acid. Therefore, the option C is incorrect.
The chemical reaction can be written as,
$Mg{\left( {OH} \right)_2}\left( s \right){\text{ }} + {\text{ }}2{\text{ }}HCl\left( {aq} \right){\text{ }} \to {\text{ }}MgC{l_2}\left( {aq} \right){\text{ }} + {\text{ }}2{\text{ }}{H_2}O\left( l \right)$

Therefore the option B is correct.

Note:
We must remember that Magnesium reacts with Carbon dioxide and forms magnesium oxide and carbon.
$Mg\left( s \right) + C{O_2} \to 2MgO\left( s \right) + C\left( s \right)$
Therefore, carbon dioxide fire extinguishers are not used for extinguishing magnesium fires. Burning magnesium is generally quenched by using a dry chemical extinguisher, or by covering the flame with sand to avoid the oxygen supply.