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:


To balance equations you have to have same number of atoms on both sides of the equation just multiply with a suitable digit
Answer:
Different types of isotopes are used for different materials or objects. For radiometric dating, uranium-235 is considered best for it while carbon-14 is used for dating of rocks. It is also used for dating of wood samples.
Explanation:
Carbon-14 and uranium-235 are used for different materials or objects for measuring the age of these materials. These two isotopes are radioactive in nature which means they emit gamma radiations which allow us to find the age of different objects. Carbon-14 has a low half life so it can be used for those objects which are present before thousands of years while uranium-235 is used for materials which are millions of years old due to high half life.
Answer: 1 mole of the substance is equal to its molar mass or vice versa.
Explanation: Example: 18 g H2O x 1 mole H2O / 18g H2O = 1 mole H2O