Your computer is slowing down because you’ve started a process that is taking most of the memory and cpu resources. which of the following commands enables you to find the process id so you can stop that process?
ps
df
du
free

ps is the command that enables you to find the process id so that you can stop that process. In fact, ps is an abbreviation of "Process Status".

Explanation:

ps is a Unix/Linux command which is commonly used to find information on current running processes in a computer. The process id will be shown in a column named "PID". The other useful information shown by the ps command includes the amount of CPU time in minutes and second that a process has been running ("TIME").

In practice, ps is used along with another Unix command, kill, to identify a target process and stop the process. Firstly, ps command is used to identify the PID of a target process (e.g. the process that consume most of the memory and CPU resources).  It is then followed with fetching the PID to the kill command to stop the process.