A balanced chemical equation shows the number of particles of each substance involved in a chemical reaction. Such an equation includes formulas and coefficients. A formula includes symbols for each type of atom in the substance. The coefficients are the numbers present in front of the formulae. If you are given a verbal description of a reaction, then you can identify the reactant and product formulae and write a balanced chemical equation with the formulae and some coefficients.
 

To be successful with this question, you need to understand what a decomposition reaction involves, be able to identify the formulae of the reactant and the products, and know how to balance a chemical equation.

In a decomposition reaction, a relative large, complex (more atoms) compound is changed into two or more products that are smaller and less complex (less atoms). In this decomposition reaction, the reactant is a compound; it is changed into two products that are elements.  

There are three steps to this question. In the first step you will have to determine the number of reactants and products. This decomposition reaction involves one reactant. This reactant decomposes into two products. Tap through the graphics until you find one that shows that many reactants and products.

The second step of this question is a bit more challenging. You will have to identify the formula of each reactant and product. The products are elements. You need to be aware that they could be diatomic elements.  There are seven elements that exist in diatomic form when they are not combined with other elements in a compound or not present in an aqueous solution. Those seven elements are hydrogen (H), oxygen (O), nitrogen (N), chlorine (Cl), bromine (Br), idoine (I), and fluorine (F). To assist in recalling this list of 7 elements, you might remember the name HONClBrIF (pronounced "Honklebriff"). 

The reactant is a compound. You need to know how to write the formula of the compound. The rules for writing formulas of compounds depend on whether the compound is a molecular compound (two non-metal elements combined) or an ionic compound (a metal element combined with a non-metal element). The rules for writing such formulas can be read using the two links below.
 
Once you have determined the formulae, it is time for the third and final step of the question - balancing the chemical equation.  This is a trial and error process that involves inserting coefficients in front of the formulae and performing an atom count to see if the number of atoms of each element is the same on opposite sides of the chemical equation. The info graphic below provides some details and a step-by-step procedure for doing this. Study the info graphic and apply the principles to balance the equation in this question.