how to use google recapcha without domain registering

[Sri Divi]

Hi All,

I am new to google recaptcha and i have the below queries.

1. is there any way i can use google recaptcha without registering the domain?
2. Can i use the captcha with in multiple pages?
3. i have an angular application which is being loaded as a widget in third party web sites in iframe/ through Js. So, i cant register all those domains. when ever a new subscription comes i can't register those domains.
4. i integrated recaptcha using angular-recaptcha and it is not allowing me to submit the form untill i verifies the captcha. 
5. is it mandatory to do server side validation.

Please suggest me with your inputs.

Thanks,

Sri