Radioactive material obeys 1st order decay kinetics,
For 1st order reaction, we have
k =

where, k = rate constant of reaction
Given: Initial conc. 100, Final conc. = 6.25, t = 18.9 hours
∴ k =

= 0.1467 hours^(-1)
Now, for 1st order reactions: half life =

= 4.723 hours.
The answer is B. Below freezing
Answer:
The heaviest element to be created by exothermic nuclear fusion is Iron
Explanation:
Because it is the heaviest element produced during fusion without having to add energy, and it is the lightest element produced during fission without having to add energy. Energy-wise, everything in the universe wants to be iron! Iron is the most abundant element on Earth, making up 34.5 percent of Earth's mass.
It is made of polar molecules
Answer: Intensive physical property
Explanation: Color is an intensive physical property since intensive properties are properties that stay the same no matter the amount of the substance is present. Blood is still red whether or not you have 2 liters of it or 4 liters.