1) Why is power delivered via AC, not DC?

In DC systems, which Thomas Edison instituted in the late 1800s, voltage dropped considerably over relatively short distances (something like 10% per kilometer). If transmitted at low voltage, AC would also incur very significant voltage drops. There was no low cost way to transform DC power to high voltage for transmission and set it down again for usage - the DC rotary-converter was expensive and high-maintenance. (Transformers, however, raised and lowered the voltage of AC power relatively conveniently, and electric power can be transmitted over long distances at high voltage with less loss of power.) Edison's solution was to have numerous DC generating facilities close to where power was consumed. This was considerably more costly than generating large amounts of AC power at big facilities, transforming, transmitting at high voltage, and transforming to usable voltage at consumption sites. Westinghouse and Tesla won the "War of Currents" against Edison. (source: Wikipedia.org: "War of Currents"

2) Still planning to use the topic of radioactive decay with a lesson involving Excel.