Uranium-235 has a half- life of 710 million years. If it is determined that a certain amount of stored U-235 will be considered safe for a particular storage area only when its radioactivity has dropped below 0.1% of the original level. Approximately how much time will this be

out of these options:

ability to burn paper

pure sodium reacting violently with water

the boiling point of water

helium does not tend to react with anything

i would say this is a physical property:

helium does not tend to react with anything

why? :

i said helium does not tend to react with anything because well, it reacts to ! but ability to burn paper, pure sodium reacting violently with water, & the boiling point of water are chemical or

physical properties: the properties of a substance that can be observed without changing the chemical makeup of the substance

chemical properties: properties of a substance relating to the chemical nature and reactivity of the substance