A60-gram sample of radioactive isotope is measured after two half-lives have passed. what pair of percentages describe the sample after two-half lives? a.) 50% unchanged and 50% stable b.) 25% unchanged and 75% stable c.) 12.5% unchanged and 87.5% stable d.) 75% unchanged and 25% stable

B.) 25% unchanged and 75% stable

Explanation:

Now, to calculate the initial amount of radioactive isotope

where,

a = amount of reactant left after n-half lives = 60 g

= Initial amount of the reactant = ?

n = number of half lives= 2

Putting values in above equation, we get:

Thus percentage of sample unchanged=

The percentage of sample decayed or has become stable=

B. 25% unchanged and 75% stable

Explanation:

Edge 2021

electrical potential energy =0.072 j

explanation:

electrical potential energy is given by

u= q δv

q= charge=6 c

δv= potential difference and is given by

δv= e d

e= electric field

d= distance=5 mm=0.005 m

δv=2.4 (0.005)=0.012 v

now electric potential energy= u= q δv

u=6 (0.012)

u=0.072 j