how would you test at the end of the reaction that the reactant you choose was indeed the limiting reactant of the system

If a hydrogen atom is neutral, it must also have  one electron. an oxygen atom (o) has an atomic number of eight (8). this means a neutral oxygen atom has eight protons and eight electrons. the element actium (ac) has an atomic number of 89, so it has 89 protons and 89 electrons in a neutral atom

The answer to the question is d

Because you ate playdough