It's chemistry not physics🥵

You're absolutely right, my apologies! It is indeed chemistry. Thanks for the correction.

For reaction b):

$$\text{CuO(s)} + \text{H}_2\text{(g)} \longrightarrow \text{Cu(s)} + \text{H}_2\text{O(l)}$$

This is a redox reaction. Specifically, it involves both reduction (of copper(II) oxide) and oxidation (of hydrogen). It can also be classified as a single displacement reaction if viewed from the perspective of hydrogen displacing copper, but redox is the more precise classification for the electron transfer.