Your question is badly written. unless you're looking for the avagrados number than its 6 x 10^23 and it means that for every one mole there that number.
Correct: The sun is the center of the solar system. It is mostly gas. It is the most massive object in the solar system.
Siliceous ooze is mostly composed of the shells of diatoms (single-celled algae) and radiolarians (single-celled animals)
Answer: B).