Answer:Strontium-90 and cesium-137 have half-lives of about 30 years (half the radioactivity will decay in 30 years). Plutonium-239 has a half-life of 24,000 years. High-level wastes are hazardous because they produce fatal radiation doses during short periods of direct exposure.
Explanation:
Answer:
Element Symbol Atomic Mass # of Atoms Mass Percent
Chlorine Cl 35.453 2 29.670%
Calcium Ca 40.078 1 16.770%
Oxygen O 15.9994 8 53.559%
Explanation:
<span>Groups are vertical, numbered 1 through 18, and have similar properties, so answer D. Most of the properties of groups are defined by the outermost electron in the shells of the elements. Horizontal delineations in the Periodic Table are known as periods.</span>
Answer:
The number of electrons in a neutral atom is equal to the number of protons. The mass number of the atom (M) is equal to the sum of the number of protons and neutrons in the nucleus. The number of neutrons is equal to the difference between the mass number of the atom (M) and the atomic number (Z).
Explanation:
69.9%
Explanation:
To find the mass percentage of iron in the compound in Fe₂O₃, we would go ahead to express the given molar mass of the iron to that of the compound.
Mass percentage = 
x 100
Molar mass of Fe = 55.85g/mol
Molar mass of O = 16g/mol
Molar mass of Fe₂O₃ = 2(55.85) + 3(16) = 159.7g/mol
Mass percentage = 
= 69.94% = 69.9%
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Mass percentage brainly.com/question/8170905
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