In "the century-old acacia tree provides a good shade to weary passersby", all the adjectives have been italicized. "century-old" needs a hyphen that was not included in the given sentence, because it is two words functioning as a single adjective.
the, brilliant, the, sixteenth
The company provides a rather wide spectrum of products.The word spectrum was introduced into the field of optics during the 17th century.
There are a hundred years in a century.
No, the word "century" is not capitalized unless it begins a sentence. So "thirteenth century" would not be capitalized in the middle of a sentence.
It has been a century since he brushed his teeth. A century ago, she was in the olympics.
The century has passed because it is now 2000.
In the 23rd century, we might have flying cars ,or perhaps we will have portals.
There are no proper nouns in the sentence. A proper noun is the name of a specific person, place, or thing. The nouns in the sentence (statues and century) are common nouns; the statues are not specified by name and a century is not a specific date.
Both are equally acceptable, equally used and equally understood
No, "mid-nineteenth century" is not capitalized unless it is at the beginning of a sentence.
Yes, all words used in the beginning of the sentence is capitalized.
The prepositional phrase in the sentence is "before the end of this century."