Answer : The amount left of leutium-176 will be, 2.10 g
Solution :
First we have to calculate the rate constant, we use the formula :

Now we have to calculate the amount left of the sample.
Expression for rate law for first order kinetics is given by :
where,
k = rate constant =
t = decay time =
a = initial amount of the sample = 16.8 g
a - x = amount left after decay process = ?
Now put all the given values in above equation, we get
Therefore, the amount left of leutium-176 will be, 2.10 g