Aspecific radioactive isotope is presented for our scientific evaluation for possible use of this isotope within the field of radioisotopic medical tracers. at 1 pm, there are 5.6 grams and at 7 pm, there are 3.2 grams. what's the half-life? a) about 3.2 hrs b) about 7.4 hrs c) about 17.1 hrs d) over 24 hrs

B)about 7.4 hrs

Explanation:  

Rate law expression for first order kinetics is given by:

where,

k = rate constant

t = time taken for decay process =6 hours

a = initial amount of the reactant = 5.6 g

a - x = amount left after decay process = 3.2 g

Putting values in above equation, we get:

To calculate the half life, we use the formula: