3 elements are present in HCOOH - hydrogen, oxygen, and carbon.
After 25 days, it remains radon 5.9x10^5 atoms.
Half-life is the time required for a quantity (in this example number of radioactive radon) to reduce to half its initial value.
N(Ra) = 5.7×10^7; initial number of radon atoms
t1/2(Ra) = 3.8 days; the half-life of the radon is 3.8 days
n = 25 days / 3.8 days
n = 6.58; number of half-lifes of radon
N1(Ra) = N(Ra) x (1/2)^n
N1(Ra) = 5.7×10^7 x (1/2)^6.58
N1(Ra) = 5.9x10^5; number of radon atoms after 25 days
The half-life is independent of initial concentration (size of the sample).
More about half-life: brainly.com/question/1160651
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Molarity = moles / liter of solution
Given, Moles of Fe³⁺ = 0.200
Volume of solution = 725 ml = 0.725 L
Conversion factor: 1000 ml = 1L
Molarity = 0.200 / 0.725 L = 0.275 M
The dissociation of Fel₃ in water is ad follows:
Fel₃ → Fe³⁺ + 3l⁻
1 mole of Fel₃ gives 1 mole of Fe³⁺ ions and 3 moles of l⁻
Since the solution is 0.275 M of Fel₃, so there are 0.275 M of Fe³⁺ ions,
and (3 x 0.275 M) = 0.825 M of l⁻ ions.
