Write the balanced equation when phosphorus burns in oxygen to form phosphorus pentoxide.

Hint: First we have to know that the mass of the products must equal the mass of the reactants in a chemical reaction (according to the law of conservation of mass)
To balance the chemical reaction, consider the unbalanced equation. Then Identify and count the atoms in both the reactants and products in the following reaction. Then to make the number of atoms the same on both the reactants and products sides, we need to add coefficients (the numbers in front of the formulas) so that the number of atoms of each element is the same on both sides of the chemical equation.

Complete answer:
Given phosphorus burns in oxygen to form phosphorus pentoxide. So, the reactants are Phosphorus (\[{P_4}\]), oxygen (\[{O_2}\]) and the product is phosphorus pentoxide \[{P_2}{O_5}\]. Then the unbalanced chemical equation is
\[{P_4} + {O_2}\xrightarrow[{burn}]{}{P_2}{O_5}\]--(1)
In the equation (1), the number of phosphorus atoms in the reactants and products are \[4\] and \[2\] respectively. Also, the number of oxygen atoms in the reactants and products are \[2\] and \[5\] respectively. So, multiply \[{O_2}\] by \[5\] and \[{P_2}{O_5}\] by \[2\]. Then the number of atoms in the reactants and products become the same.
Hence, the balanced chemical equation is
\[{P_4} + 5{O_2}\xrightarrow[{burn}]{}2{P_2}{O_5}\]

Note:
Note that the two main forms of phosphorus are white phosphorus and red phosphorus. Representation of a chemical reaction in terms of symbols and chemical formula of the reactants and products taking part in the reaction is known as a chemical equation. Combination, Decomposition, Single-replacement, Double-replacement, and Combustion are the five basic types of chemical reactions.