Answer:
0.88
Explanation:
Step 1 Obtain the decay constant(λ) from
t1/2 = 0.693/λ
λ = 0.693/t1/2
t1/2 = half life = 6.76 min = 405.6 secs
λ = 0.693/405.6 secs
λ = 0.0017 s-1
Step 2 Obtain the fraction left at a time t
From
N= Noe^-λt
Where;
N= mass of radioactive material left after a time t
No = mass of radioactive material originally present
λ = decay constant = 0.0017 s-1
t= time taken = 75.1 secs
Hence;
N/No = e^-0.0017 * 75.1
N/No = 0.88
Note; N/No is the required fraction left after 75.1 seconds
