At max how many records does a process variable can store.? ...

Can you be a bit more descriptive of what you mean by records a PV can store?

Hi Satya, I have to extract data from a excel sheet which has more than 35K rows and store the extracted CDT format data into a PV.

Is there a reason you want everything stored in a single PV? There are plug-ins that would allow you to extract info from Excel and store them in a database. Have you considered them?
You data size is set my the MAX_DATA_SIZE variable that you set in the configuration file. To my best understanding, you can store a large volume of data in a PV but that is not a recommended Appian best practice. You should consider storing the data in a database table and use the info as required.
Hope this helps