Question

When magnesium is burnt in presence of air the weight of magnesium:
A) Increases
B) Decreases
C) Does not change
D) Increases then decreases

Answer 1

We have to know that in chemistry, periodic tables play a vital role. In the periodic table totally $118$ elements. In the periodic table totally $18$ columns and $7$ rows. The columns are called as groups. Hence, $18$ groups in the periodic table. The rows are called periods. Hence, the total $7$ period in the table. Magnesium is present in the second group and the oxygen is present in the sixteenth group of the periodic table.

Complete answer:
We also need to know that the atomic number of magnesium is $12$. It is one of the alkaline earth metals in the periodic table. It is present in the third period and second group in the periodic table. The symbol of magnesium is ${\text{Mg}}$.
The atomic number of the oxygen is $8$. It is present in the second period and sixteenth group in the periodic table. The symbol of oxygen is ${\text{O}}$.
${\text{2Mg + }}{{\text{O}}_{\text{2}}} \to {\text{2MgO}}$
The initial mass of the magnesium only depends on the atomic weight of the magnesium atom. After magnesium is reacted with air to give magnesium oxide. Hence, the weight of magnesium increases.
Hence, option A is correct, because after the reaction magnesium weight is increased.
Option B is not correct, because after the reaction weight of magnesium is not decreased.
Option C is not correct, because after the reaction weight of magnesium is changed.
Option D is not correct, because after the reaction weight of magnesium is increased.

Note:
We also remember that the atomic number of the atom depends on the number of protons or the number of electrons. The atomic number of the atom is equal to the number of protons or the number of the electrons. The mass number of the atom depends on the number of protons and the number of neutrons. The mass number of the atom is equal to the sum of the number of protons and the number of neutrons in the atom. The oxidation reaction means addition of oxygen or the removal of hydrogen or the loss of electrons. The reduction reaction means addition of hydrogen or the removal of oxygen or the gain of electrons.