What word names a piece of rice or a tiny speck of sand?

Which physicist, reflecting on the atomic bomb, reportedly said in 1955, "If only I had known, I would have become a wa… A standard piano has 52 white keys and how many black keys? A picture of which actress, "the Love Goddess", adorned an atomic bomb tested at Bikini Atoll in 1946? What word names a piece of music or a short school essay? What was the name for the pigtail that was once required in the British Army? Which pilot radioed in 1937: "Gas is running low... we are flying at 1,000 feet"? The pilot's wife in 1986's "Top Gun", Meg joined the military herself in which 1996 film? A pine, a fir and a spruce are all what kind of tree?