Scott Schpber, age 11, of Shreveport, Louisiana, for his question:
What color is liquid hydrogen?
At normal temperatures, hydrogen is a colorless, odorless gas. When its temperature is reduced below minus 253 degrees centigrade, it becomes a colorless, odorless liquid. If its temperature is reduced another six centigrade degrees, the colorless liquid becomes a glassy solid ice. Hydrogen is certainly not a colorful chemical element. But it has one surpassing feature. The hydrogen atom happens to be the smallest and lightest of all atomic elements.
At temperatures above minus 423 degrees Fahrenheit, it boils and becomes the lightest of the gases. Ordinary air is 14 times denser and heavier than hydrogen gas. Liquid hydrogen is less dense than all other liquids. Its weight is merely about 70 grams per liter. No other solid is as light as solid hydrogen, which has a wispy weight of only 88 grams per liter. To some extent, these properties are due to the small hydrogen atom. It rates as atomic number one because its nucleus has but one proton, orbited by one electron.