The table shows the amount of radioactive element remaining in a sample over a period of time: What is the half-life of the element in hours?
Group of answer choices
a. 63 hours
b. 7 hours
c. 21 hours
d.14 hours

An atom of which element reacts with an atom of hydrogen to form a bond with the greatest degree of polarity ?

Large helium-filled balloons are used to lift scientific equipment to high altitudes. what is the pressure inside such a balloon if it starts out at sea level with a temperature of 10.0ºc and rises to an altitude where its volume is twenty times the original volume and its temperature is – 50.0ºc ?

About 3% of the water on earth is freshest. only about 40% of that freshwater is available for human use. why is so much freshwater unavailable for human use?