Which of the following keys is used to replace a single character with new text?

Solution (By Examveda Team)

In Unix command line editors like vi or Vim, the s key is used in the command mode to replace a single character under the cursor with new text. After pressing s, you can enter the replacement text, and the character under the cursor will be replaced with it.
So, s is the correct key to replace a single character with new text.