Sodium-25 after 3 minutes : 1.0625 mg
<h3>Further explanation</h3>
General formulas used in decay:

T = duration of decay
t 1/2 = half-life
N₀ = the number of initial radioactive atoms
Nt = the number of radioactive atoms left after decaying during T time
<h3 />
No=8 mg
t1/2=60 s
T=3 min=180 s

In the equation given above, there is conservation of MASS, CHARGE AND ENERGY.
These three parameters are usually conserved during the course of chemical reactions. When any of these parameter experience a reduction during the course of chemical reaction, such loss is always gained by other elements involved in the same reaction, so that at the end of the day, they are not considered as lost.
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Answer:
The answer to your question is Pressure = 5 atm
Explanation:
Data
Volume 1 = V1 = 0.5 l
Pressure 1 = P1 = 1 atm
Volume 2 = V2 = 0.1 l
Pressure 2 = P2 = x
Formula
To solve this problem use the Boyle's equation
V1P1 = V2P2
Solve for P2
P2 = V1P1/V2
Substitution
P2 = (0.5 x 1) / 0.1
Simplification
P2 = 0.5/0.1
Result
P2 = 5 atm
Answer:
Zinc metal might be mixed with the copper.
Explanation:
Density is defined as mass of the substance present in the unit volume of the substance.

Density of pure copper = d = 8.94 g/mL = 

Mass of the copper penny = M = 2.49 g
Volume of the copper penny = V = 
Density of the copper penny = d

Density of pure copper > Density of zinc > Density of penny

The metal mixed with copper is zinc to make a penny . This is so because all the other metal given have higher value of density which will increase the density of the copper penny if they were present.
But here the density of the copper penny is smaller than density of pure copper which means that less denser metal than copper is also added in the penny.