How to hide Price on certain categories?

Where do you want to hide it? In the [adverts_add] form when a category is selected or on Ad details page?

when i use the code [adverts_list] it displays all the ads with thier price . i want to hide the price for a certain category . is this doable?

You would need to edit wpadverts/templates/list-item.php template file and modify it so the price field will be hidden depending category on the category to which the Ad is assigned.

Also before modifying the file consider creating a child template as explained here https://wpadverts.com/documentation/child-themes-and-templates/, so the file will not be overwritten on WPAdverts update.