Can we add department while creating 'product item' in the Quickbooks Online?

Welcome to the Community, @chetan003.

I can provide some information about creating items in QuickBooks Online.

Yes, you can add departments to your products and services. I suggest enabling the Class tracking feature and use it when creating an inventory.

Here's how:

1. Click the Gear icon in the upper-right.
2. Select Account and Settings.
3. Go to the Advanced tab.
4. Enable Track classes. 
5. Press Save, then hit Done.

Once done, the option will now be available when you create or edit an inventory in QuickBooks (see screenshot below).

Meanwhile, I've attached some articles you can use to learn more about class tracking, like how to enable and use them for your inventory:

• Turn on class tracking in QuickBooks Online
• Get started with class tracking in QuickBooks Online
• Create and manage classes in QuickBooks Online

Please know that I'm just a post away if you have any other questions. Have a great day ahead.