I have iphone4 not support WhatsApp

rithik256 wrote:

iOS version is 7.1.2 can I update iOS 9

No. An iPhone 4 cannot update beyond iOS 7.1.2, and no Whatsapp is no longer compatible with an iPhone 4.

Its an almost 10 year old device at this point.

WhatsApp is not an Apple product. Contact the app developer here --> App Support