Explanation:
It is the heat required to change a gram of substance from a liquid to a gas.
The mass decay rate is of the form

where
m₀ = 3000 g,the initial mass
k = the decay constant
t = time, years.
Because the half-life is 30 years, therefore

After 60 years, the mass remaining is

Answer: 750 g
The amount of energy required to change the temperature or phase of a reactant
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Viscosity is the thickness of a liquid, cause by the friction between the molecules in that liquid. A very high viscosity would result in a solid form and low would be a liquid. If a liquid as zero viscosity is only found in superfluids at there freezing points or lower. There are also two types of viscosity “dynamic” (which is measure in seconds, pascal seconds to be exact) and “kinematic” (which is measured in metre per second squared)
Fun fact they use viscosity to predict when volcanoes are going to erupt:)
Hope this helps I love sciencey stuff so if you need anymore help let me know!