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.
Hydrogen Carbonate, or HCO3.
Mass number = number of protons + number of neutrons
mass number= 8 + 7= 15 ---> the answer is B.
(acetone) has a molecular ion at m/z = 58, an infra red absorption at 1650cm^-1
Acetone is a synthetic substance that is also naturally present in the environment. It is a tasteless, colourless liquid with a distinct odour. It is combustible, readily evaporates, and dissolves in water. It is also known as beta-ketopropane, 2-propanone, and dimethyl ketone. Plastic, fibres, medications, and other compounds are all made from acetone.
Other substances can also be dissolved with it. It is a byproduct of the breakdown of human fat and is found naturally in plants, trees, volcanic gases, forest fires, and other organisms. It can be found in landfills, tobacco smoke, and automobile exhaust. Acetone is released into the environment more through industrial processes than through natural ones.
Learn more about acetone here;
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