Based on the clue 'a 250 million year old grayish white limestone lay...', what is the answer?

Based on the clue 'a 24 carat stone weighs 48 of these metric units', what is the answer? What is associated with: a 25 headless shark monument was installed in england aug 9 1986 anniversary of the dropping o… Based on the clue 'a 25 pound heart helps pump the blood to its head...', what is the answer? What is associated with: a 25 year long telescope search for it ended with its discovery in 1930? Based on the clue 'a 25th anniversary is a silver this', what is the answer? Based on the clue 'a 2nd verse to this rhyme begins every fiddler he ...', what is the answer? What is associated with: a 3 cent stamp of 1956 honored the 50th anniversary of this wyoming national monument? Based on the clue 'a 3 legged stand on which to rest your portable me...', what is the answer?