Different between open source software and licensed softwares?

Answer me pls is an algorithm that has been coded into something that can be run by a machine.

You are almost finished updating a web site. as part of the update, you have converted all pages from html 4.0 to html5. the project is currently on schedule. however, your project manager has been asked by the marketing team manager to justify a day of time spent validating the site's html5 pages. the marketing team manager does not have technical knowledge of the internet or the web. which is the most appropriate explanation to provide to the marketing team manager?

State 7 common key's for every keyboard