Answer is: mass number of element is 234.
<span>Alpha particle is nucleus of a </span>helium-4<span> atom, which is made of two </span>protons<span> and two </span>neutrons<span>.
</span>²³⁸U → ²³⁴Th + α (alpha particle).
Alpha decay is radioactive decay<span> in which an </span>atomic nucleus<span> emits an </span>alpha particle<span> (helium nucleus) and transforms into an atom with </span>an atomic number that is reduced by two <span>and </span>mass number<span> that is reduced by four</span><span>.</span>
Yes it is a chemical change because it is changing color which shows a chemical change, plus it changes into another element
The radioactive decay follows first order kinetics
The integrated rate law expression for first order rate is
ln(A / At) = kt
Where A= initial concentration
At=concentration at time "t"
t = time
K= rate constant
ln(50 / 0.0488) = k X 38
Therefore
K = 0.1824 day-1
The relation between rate constant and half life is
So half life = 0.693 / 0.1824 = 3.8 days
So isotope must be Radon-222
Answer:- D. 
Explanations:- In chemical equations, (aq) stands for aqueous, (l) stands for liquid, (g) stands for gas and (s) stands for solid. In double replacement reactions, (aq) means soluble and (s) means insoluble that is precipitate.
Looking at all the equations, it is only the last equation that has a solid product and so this is the only precipitation reaction. A precipitate for Iron(II)carbonate is formed in it.
