Question

A sample contains 2.2 g of the radioisotope niobium-91 and 15.4 g of its daughter isotope, zirconium-91.

Answer 1

Time to decay : 2040 years

Further explanation  

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  

General formulas used in decay:  

$\tt Nt=No.\dfrac{1}{2}^{\dfrac{T}{t\frac{1}{2} }$  

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  

moles zirconium :

$\tt \dfrac{15.4}{91}=0.169$

moles niobium :

$\tt \dfrac{2.2}{91}=0.0242$

the half-life of niobium-91 is 680 years

Reaction

⁹¹₄₁Nb ⇒⁹¹₄₀Zr + ₁⁰e

Amount of Nb from reaction : 0.169

Amount of initial Nb = 0.0242 + 0.169 = 0.1932

Time to decay (T) :

$\tt 0.0242=0.1932.\dfrac{1}{2}^{\dfrac{T}{680}}\\\\0.1252=\dfrac{1}{2}^{\dfrac{T}{680}}\\\\\dfrac{1}{2}^{3}=\dfrac{1}{2}^{\dfrac{T}{680}}\\\\T=680\times 3=2040$

Answer 2

Answer:

It’s CCCCCCCCCCCCCCC

Explanation:

I just took the instruction and yes its “C.”