Whatsapp

WhatsApp requires a cellular telephone for the app. An iPad is not a cellular telephone and cannot connect to any cellular telephone service providers voice call network, so WhatsApp does not support it.

You can use WhatsApp web with an iPad if you already have a cell phone and a WhatsApp account.

The developer of WhatsApp has not created a version for the iPad.

Yes, in some cases developers create apps that are compatible with both devices, sometimes compatible only with iPhone, and sometimes compatible only with the iPad.