کدوم توجمله زیر درسته ؟

"Who is responsible" is the correct  one to use.

In this question we shouldn't  use "the" before  "responsible". Because  responsible is being used as an adjective to describe the subject of the question. In English, we usually don't use an article before an adjective in this context.

Article:     (a, an, the)حرف تعریف مثل