der Brocken
chunk
A large, irregular piece of something solid, for example rock, bread, or ice.
Er brach einen großen Brocken vom Brotlaib ab.
He broke off a large chunk from the loaf of bread.

chunk
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chunk
A large, irregular piece of something solid, for example rock, bread, or ice.
Er brach einen großen Brocken vom Brotlaib ab.
He broke off a large chunk from the loaf of bread.

'Brocken' (chunk) is closely related to the verb 'brechen' (to break). A 'Brocken' is literally a piece that has been broken off from something larger. This origin helps you understand the basic meaning.
Ein Steinbrocken löste sich von der Felswand.
A chunk of rock came loose from the cliff face.
When 'Brocken' (chunk) refers to a piece of something, the noun naming the material often follows directly without an article. Typical patterns are 'ein Brocken Brot' (a chunk of bread), 'ein Brocken Käse' (a chunk of cheese), or 'ein Brocken Gestein' (a chunk of rock).
Zum Wein reichte er einen Brocken Käse.
He served a chunk of cheese with the wine.
In the meaning of 'schwierige Aufgabe' (difficult task), 'Brocken' is colloquial. You often hear it in combinations like 'ein harter Brocken' (a tough nut/a hard challenge) or 'ein dicker Brocken' (a big challenge).
Diese Aufgabe ist ein wirklich harter Brocken, ich weiß nicht, wo ich anfangen soll.
This task is a really tough challenge; I don't know where to start.
To describe a person or thing as big and heavy, the structure 'ein Brocken von einem/einer ...' (a hulk/lump of a ...) is often used. This emphasizes the impressive size.
Der neue Schrank ist ein riesiger Brocken von einem Möbelstück.
The new cabinet is a huge lump of a piece of furniture.
When 'der Brocken' is used as the name of the mountain in the Harz region, it almost always appears with the definite article 'der'. The context is usually geography, hiking, or weather.
Die Aussicht vom Brocken war fantastisch.
The view from the Brocken was fantastic.
problem
'das Problem' and 'der Brocken' can both mean a difficult task or difficulty. 'das Problem' is neutral and fits in almost all situations. 'der Brocken' is colloquial and emphasizes that something is especially big, difficult, or unpleasant. It is often used for a task that takes a lot of work, or for information that is hard to accept. The words can be confused because both name a difficulty. However, 'Brocken' sounds figurative and more casual, not as neutral as 'Problem'.

Im Gespräch merkt man schnell, dass dieses Projekt ein echter Brocken ist.
In conversation, you quickly notice that this project is a real tough challenge.
Hannah hat ein Problem mit dem Busplan und kommt morgen vielleicht zu spät.
Hannah has a problem with the bus schedule and might be late tomorrow.