PHP web form validation and protection

Hello, we need someone to help us with php web form validation.
The form code itself will be external, not on the same page!
This means, the form is on the page contact.php, but the form action is /inc/contact. inc. php.

The web form consists of the following inputs:
radio
radio
text/name - required
email - required
message - required
checkbox - required

We need form validation for the following:
- Is the Name only characters and white space? Not numbers/special characters.
- Is the email in the right format?

We need protection for the following:
- Special characters like < > etc will be converted to html characters, so they can not be used to send malicious code like <script> tags, or <a> links.

- A simple random math question (like "what is 2 + 7?") to prevent bot spam. Or a different alternative, if you have one. NOT google recaptcha though.


If the validation is unsuccessful, different divs will be displayed depending on the error. We have already created these.


Please attach examples of previous web forms you coded.