When to use No and Nope

Question

As per what I understand Nope is an informal way of expressing the same what no does.
Is it appropriate to use Nope in official mails, or is it suggested to use in like whatsapp chat etc.

Also why the need for this separate word Nope?

Answer 1

As per what I understand Nope is an informal way of expressing the same what no does.

Yes, but only when 'No' is used as an exclamation. So you can't replace 'no' with 'nope' in 'I have no words....'.

Is it appropriate to use Nope in official mails, or is it suggested to use in like whatsapp chat etc.

It isn't appropriate to use 'Nope' in a formal setting. However, you can use it in informal setting like WhatsApp, FB, Instagram chats etc.

Also why the need for this separate word Nope?

The P in 'nope' has been inserted for articulatory reasons. When you say 'No' (exclamation), you would usually pause and your lips would come close to each other which results in an unreleased bilabial¹ stop, [p̚].

• No → [nəʊ] + unreleased bilabial stop [p̚] → [nəʊp̚] ('nope')

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^{1. Bilabial sounds are ones tha are articulated with both lips such as /p b m/ etc.}