Immediately! is the chemical reaction 4ai + 202 --> 2ai203 balanced?

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.