Final answer:
When an economics professor buys a US government bond from you, it decreases banking reserves and the money supply, analogous to when the central bank sells bonds, reducing money in circulation.
Step-by-step explanation:
If your economics professor buys a US government bond from you, the effect will be to decrease banking reserves and decrease the money supply. This concept can be better understood by considering the central bank's actions. When the central bank purchases bonds, it causes money to flow from the central bank to individual banks, increasing bank reserves and the money supply. Conversely, when the central bank sells bonds, money flows from individual banks into the central bank, thus reducing bank reserves and the money supply. Since your economics professor is part of the individual or non-governmental sector, the transaction is similar to the latter scenario, where selling the bond is effectively taking money out of circulation, leading to a decrease in the money supply.