The half-life of I-131 is 8.0 days. If a medical treatment involves a dose of 100. mg of I-131, how much of the isotope remains after 16 days?
A) 12.5 mg
B) 25.0 mg
C) 50.0 mg
D) 75.0 mg
B
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The sea is salty because
A. the mantle is salty. B. rainwater is salty. C. marine organisms manufacture salts. D. it contains salts from Earth's crust that have been dumped into the ocean and dissolved.
Give an example of two ways humans have made major modifications to the Mississippi River system
What will be an ideal response?
With daytime temperatures that can reach 430°C, why is nighttime on Mercury so cold?
A. With very little atmosphere, heat is quickly lost back into space. B. The solar winds quickly dissipate all heat on the planet's dark side. C. Because the year is so short, there isn't enough time for the heat to build up in the equatorial regions. D. The weak gravitational field doesn't retain the daytime's heat.
Which of the following is NOT a drawback of using windmills for energy?
A. Windmills are not always visually appealing. B. Windmills kill birds. C. Wind is not always constant. D. Windmills cannot be placed on shorelines.