Write a balanced chemical equation for the following chemical reaction :
Magnesium burns in oxygen to from magnesium oxide.

Explanation

Magnesium burns is oxygen (of air) to from magnesium oxide. This reaction can be written in the form of a word equatin as:
Magnesium + Oxygen `to` Magnesium oxide
Now, Symbol of magnesium is Mg
Formula of oxygen is `O_(2)`
And, Formula of magnesium oxide id MgO
By putting these symbols and formulae in the above word equation, we get the following chemical equation:
Mg + `O_(2) to` MgO
Let us balance this equation now, We can see from the above equation that there are 2 oxygen atoms on left side but only 1 oxygen atom on the right side, we write 2MgO. Thus,
Mg + `O_(2)to` 2MgO
Now, we have 1 magnesium atom on left side put 2 magnesium atoms on the right side. To have 2 magnesium atoms on the left side, we write 2Mg. This gives us:
2Mg + `O_(2)to` 2MgO
This equation contains an equal number of Mg atoms and O atoms on both the sides, so this is a balanced equation.
Magnesium is a solid, oxygen is a gas and magnesium oxide is also a solid. So, we can write the above chemical equation with state symbols as follows:
2Mg (s) + `O_(2)to` 2MgO (s)