Scientific laws and theories have different jobs to do. A scientific law predicts the results of certain initial conditions. ... In contrast, a theory tries to provide the most logical explanation about why things happen as they do.
Answer:
the smallest mass of material that can sustain a chain reaction
Explanation:
Critical mass refers to the smallest possible mass of a fissionable material that can sustain a chain reaction
H2O is the chemical formula of water. It means that each molecule of water is made up of two hydrogen atoms, indicated by the letter H, and a single oxygen atom, represented by the O. Water is a chemical substance with no smell, taste, or color.
Answer:

Explanation:
The question will be easier to solve if we interpret it as, " How long will it take until one-fourth of a sample of the element remains,?"
The half-life of the element is the time it takes for half of it to decay.
After one half-life, half (50 %) of the original amount will remain.
After a second half-life, half of that amount (25 %) will remain, and so on.
We can construct a table as follows:

