By the time the universe was a few minutes old, helium production had effectively ceased.What does the passage mainly explain A.How stars produce energy.B.The difference between helium and hydrogen.C.When most of the helium in the universe was formed.D.Why hydrogen is abundant. 点击查看答案...
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Helium:Helium is one of the most abundant elements in the universe. Only hydrogen is more abundant. Both helium and hydrogen are components of stars and the gas giant planets.Answer and Explanation: Helium has an atomic weight of 4.003. Its atomic number is 2, indicating that there are 2 ...
The energy, say, uh...radiated into space by a normal, so-called "main sequence" star, is...generated by the uh...the conversion of hydrogen to helium. Here, you may ask what a main sequence star is. OK...the main sequence refers to a major grouping of stars that uh... forms...
In the exosphere, the atmosphere becomes exceedingly thin, with gas molecules spread out over vast distances. Unlike the denser layers of the atmosphere closer to Earth, the exosphere contains very few particles, primarily lightweight gases such as hydrogen and helium. These particles are so sparse...
Identify the elements that have molecules as their basic units. a. Hydrogen. b. Iodine. c. Lead. d. Oxygen. Which of the following pairs of elements are likely to form an ionic compound? a. helium and oxygen b. magnesium and chlorine c. chlorine and bromine d. potassium and sulfu...
Space is mostly a vacuum, containing low densities of particles, predominantly hydrogen and helium, and fields such as gravitational and electromagnetic fields. 15 How big is the universe? The observable universe is about 93 billion light-years in diameter, but the entire universe may be much lar...
It took 380,000 years for the universe to cool enough to slow down the electrons so that the nuclei could capture them to form the first atoms. The earliest atoms were primarilyhydrogenandhelium, which are still the most abundant elements in the universe, according toJefferson Lab. Gravity ev...
The periodic table of elements lists all the atoms that are currently known and available. Being that the elements are the most basic and simplified form of any substance, all elements are atoms. Some examples are helium, oxygen and hydrogen. ...
Living things, for example, are mostly made from the atoms carbon, hydrogen, and oxygen. These are just three of over 100 chemical elements that scientists have discovered. Other elements include metals such as copper, tin, iron and gold, and gases like hydrogen and helium. You can make ...