<span>Now, multiply one or both equations by small numbers to make the number of electrons the same in the two half reactions. In this case, multiply the top equation by 2 and the bottom one by 7 to give you 14 electrons in each half reaction: </span>
<span>Finally, add the two half reactions and simplify by cancelling anything that is on both sides. This will give you the final balanced reaction: </span>
<span>2 NO2 + 7 H2 --> 2 NH3 + 4 H2O </span>
<span>So, the answer to the original question is (A) 7 </span>