Im not sure but here is some information to help A declarative question is a yes-no question that has the form of a declarative sentence but is spoken with rising intonation at the end. Declarative sentences are commonly used in informal speech to express surprise or ask for verification.
The amount left after 20 years = 154.15 mg
<h3>Further explanation
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The atomic nucleus can experience decay into 2 particles or more due to the instability of its atomic nucleus.
Usually radioactive elements have an unstable atomic nucleus.
The main particles are emitted by radioactive elements so that they generally decay are alpha (α), beta (β) and gamma (γ) particles
The decay formula for isotope :

Then for t=20 years, the amount left :

If X is an equivalent base to H₂O
HX is an equivalent acid to H₃O⁺
HX is a stronger acid than H₃O⁺
HX is not an acid
X⁻ is a stronger base than H₂O
HX is a weaker acid than H₃O⁺
X⁻ is a weaker base than H₂O
X⁻ is not a base.
The correct response or this is
X⁻ is a stronger base than H₂O
HX is a weaker acid than H₃O⁺
A solution is the answer to a problem