Q.1
1.Holocaust, denial
The Holocaust and denial of history must never be ignored
The sentence is grammatically correct so they belong to the same category nouns.
2.Needless, repetition
The speech was full of needless and repetition making it boring.
Needless is an adjective it describes something ,and repetition is a noun it is a thing.
These do not belong to the same category
3.Horrific,Destructive
The storm was both horrific and destructive
Both "horrific" and "destructive" are adjectives because they describe the storm
Q.2
1.The view from the mountain top was breathtakingly incredible
2. She is a well-known author in the literary world.
3. The question was open-ended allowing for many different answers
4.The dog made a high-pitched sound when it barked
5.The company is well-established in the tech industry.
kamal