The correct answers are Which platform is for the express train? and What time does the station close?

Which and What can both be used directly before a noun to ask a question.

Use Which + noun when there is a limited number of choices (like platforms in a station).

Use What + noun when asking a general question with many possible answers (like time).

"How" cannot be used directly before a noun like this, and "Which of" must be followed by a determiner (like "the" or "these").