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
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No=8 mg
t1/2=60 s
T=3 min=180 s

HNO3 and H2SO4 are Arrhenius acids which will increase the concentration of H+ when dissolved in water.
KOH and Ca(OH)2 are Arrhenius bases that increase the concentration of OH- when dissociated in water.
Explanation:
The degree of unsaturation is given as;
Degree of unsaturation = (2C + 2 + N - H - X) / 2
(a) C5H6
Using the formular above;
Degree of unsaturation = [ 2(5) + 2 - 6] / 2
Degree of unsaturation = [ 12 - 6 ] / 2 = 3
(b) C10H6Cl2
Using the formular above;
Degree of unsaturation = [ 2(10) + 2 - 6 -2 ] / 2
Degree of unsaturation = [ 22 - 8 ] / 2 = 7
(c) C4H3NO
Using the formular above;
Degree of unsaturation = [ 2(4) + 2 - 3 -1 ] / 2
Degree of unsaturation = [ 10 - 4 ] / 2 = 3
Note: Oxygen is ignored because its presence has no effect on the degree of unsaturation.