What is the best way to write the words in bold in sentence 7? (7) His first major find was discovery of the planet Uranus in 1781

You failed to provide any bold-faced words, so all I can do is correct the sentence as it should be written.

His first major find was the discovery of the planet Uranus in 1781.

Add the word 'the' and a period as shown. And, technically, if Uranus is already understood to the listener/reader, then the word 'planet' is redundant.