Answer:- 9.4 minutes.
Solution:- Radioactive decay obeys first order reaction kinetics and the equation used to solve this type of problems is:
where, k is decay constant and t is the time. 
is the initial amount of the radioactive substance and N is the remaining amount.
Since the value of decay constant is not given, so we need to calculate it first from given half life by using the formula:
where 
stands for half life.
Given half life is 3.0 minutes.
So, 
Let's plug in the values in the first order reaction equation and solve it for t.
It could also be written as:
k = 9.4 min
So, the radioactive substance would take 9.4 minutes to decay from 40.0 grams to 4.5 grams.
I would say that descriptive investigations aren't repeatable because it means that you are only describing something - you ask certain question about something, but do not form a hypothesis at that point yet. So it would be a waste of time to simply ask the same questions over and over again with no hypothesis to prove, which is why these types of investigations cannot be repeated.
Answer:
The phases of the Moon depend on the moon's position compared to the Earth and the Sun. Remember that the moon revolves around the Earth. As the moon goes around the Earth, half of the moon is always illuminated by the Sun.
Here we have to get the temperature and pressure at which helium gas mostly behaves as ideal gas.
Helium (He) behave most like an ideal gas upto 24K temperature and 0 atm pressure.
The deviation of a real gas to ideal gas occurs at high temperature and low pressure.
The deviation of ideal gas to real gas occurs on taking into account the van der waals' force of attraction between the gas molecules. Now, the van der waals' interaction depends upon the polarisibility of the gas molecule.
As helium (He) is non-polarisable and very small (atomic number 2) it mostly behaves as ideal gas upto 24K temperature and 0 atm pressure.
Although the deviation from the ideal gas behavior to real gas is not so prominent at little high temperature also. Upto 50K it mostly behaves like an ideal gas.
E=x +c - D Emonety to explain the functionally full process of work and C3
