3.) underline ( )CH_(4)+underline ( )O_(2)arrow underline ( )H_(2)O+underline ( )CO_(2)

## Step 1<br />The given chemical equation is \(CH_{4} + O_{2} \rightarrow H_{2}O + CO_{2}\). This equation represents the combustion of methane (CH4) in the presence of oxygen (O2) to produce water (H2O) and carbon dioxide (CO2).<br /><br />## Step 2<br />To balance this chemical equation, we need to ensure that the number of atoms of each element is the same on both sides of the equation. This is in accordance with the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction.<br /><br />## Step 3<br />Looking at the equation, we can see that there are 4 hydrogen atoms in CH4 and 2 hydrogen atoms in each H2O molecule. Therefore, we need 2 H2O molecules to balance the hydrogen atoms.<br /><br />## Step 4<br />Now, we have 4 hydrogen atoms on the right side of the equation, but only 1 carbon atom in CH4 and 1 carbon atom in CO2 on the left side. Therefore, the equation is not balanced yet.<br /><br />## Step 5<br />To balance the carbon atoms, we need to have 2 CO2 molecules on the right side of the equation. This gives us 2 carbon atoms on both sides of the equation.<br /><br />## Step 6<br />Finally, we need to balance the oxygen atoms. On the left side, we have 2 oxygen atoms in O2 and 2 oxygen atoms in 2 CO2 molecules, giving us a total of 4 oxygen atoms. On the right side, we have 2 oxygen atoms in 2 H2O molecules and 2 oxygen atoms in 2 CO2 molecules, giving us a total of 4 oxygen atoms.