Breakdown of Я решил разобрать старый хлам на чердаке.
я
I
старый
old
на
on, at / by (transport) / to (a place) / to (in answer to)
решить
to decide (perfective)
Questions & Answers about Я решил разобрать старый хлам на чердаке.
Could I use the lesson's focus word всякий with the word хлам in this sentence?
Absolutely. Saying всякий хлам (all sorts of junk / all manner of rubbish) is a very common Russian phrasing. It emphasizes the random, mixed nature of the items up there. You couldn't use каждый (every) here, because каждый refers to individual, distinct countable items, whereas хлам is a mass noun.
I thought разобрать meant 'to disassemble' or 'to take apart'. Why is it translated as 'to sort out'?
While разобрать does mean 'to take apart' (like a machine or an engine), when you apply it to a mess, a closet, or хлам (junk), it means 'to sort out', 'to declutter', or 'to tidy up'. The logic is that you are taking a chaotic pile apart piece by piece to organize it or decide what to throw away.
Why is it на чердаке instead of в чердаке for 'in the attic'?
Чердак (attic) is one of those traditional space words that takes the preposition на instead of в, even though it's an enclosed room. It acts as an exception, following the same pattern as на кухне (in the kitchen) and на балконе (on the balcony). It is in the prepositional case here because it answers the question 'where?'
Can I make хлам plural if there are multiple piles of junk?
No, хлам is an uncountable noun and is only ever used in the singular. This works exactly like the English words 'junk' or 'rubbish'.