The half-life of na-24 is 15 hours . when there are 1000 atoms of na-24 in a sample , a scientist starts a stopwatch . the scientist stops the stopwatch at 45 hours , there are atoms of na-24 remaining

Answer : The atoms of Na-24 remaining are, 125.1 atoms

Explanation :

Half-life = 15 hours

First we have to calculate the rate constant, we use the formula :

Now we have to calculate the left atoms of Na-24.

Expression for rate law for first order kinetics is given by:

where,

k = rate constant  =

t = time passed by the sample  = 45 hours

a = initial atoms of the reactant  = 1000

a - x = atoms left after decay process = ?

Now put all the given values in above equation, we get

Therefore, the atoms of Na-24 remaining are, 125.1 atoms

the answer is na (sodium)

yes the answer is total mass in unchanged   : )