May 06 2021
My excel scatter graphs do not show an option to add y-axis title or x-axis title.
May 07 2021
The Chart Elements popup only has an option to add both axis titles (the second check box).
If you want to add only one of the two, you can add both, then click on the one you don't want and press Delete.
Or activate the Design tab of the ribbon (under Chart Tools) and click Chart Element > Axis Titles, then select the option you want.