@Karthik R Hello and welcome to Microsoft Q&A.
I understand you are having difficulty deleting your spark pool.
The important clue here is the Azure Cloud Shell's error message.
Notebook 1
is referencing your Spark1
. If the pool Spark1 was deleted, then the Notebooks attatched to it will break.
Solution: Go to the Notebook 1 and change the Attatched to
and then publish. Then try deleting the spark pool.