Learn Russian: Никто не знает, чьи ордена вчера вручал министр. - No one knows whose medals the minister was awarding yesterday.

This is a classic example of a noun with two distinct plural forms. The form ордена (stressed on the final syllable) means "medals" or "decorations", which fits this context. The alternative plural ордены (stressed on the first syllable) means "orders" in the sense of historical, fraternal, or religious organizations, such as monastic or knightly orders.

What case is the phrase чьи ордена in?

It is in the accusative case because it is the direct object of the verb вручал (was awarding). Since орден is an inanimate noun, its plural accusative form is identical to its plural nominative form.

Why is the subject министр placed at the very end of the sentence?

Russian uses flexible word order for flow and emphasis. In a subordinate clause like this, the question words (чьи ордена) must come first. Following them directly with the verb (вручал) and placing the subject (министр) at the end is a very natural Object-Verb-Subject pattern that smoothly resolves the clause.

Why use the imperfective verb вручал instead of the perfective вручил?

The imperfective вручал emphasizes the ongoing process or the extended activity of handing out the medals over a period of time yesterday (matching "was awarding"). If the sentence used the perfective вручил, it would frame the action as a single, completed event ("awarded").