(a(i))[2]
State the meaning of radioactive.
(a(ii))[2]
State the meaning of decay constant.
(b)[2]
A sample of water has been contaminated with iodine-131. The activity of the iodine-131 in $1.0\text{ kg}$ of water is $560\text{ Bq}$. Determine the number of iodine-131 atoms in $1.0\text{ kg}$ of water.
(c)[3]
The regulations say that the activity of iodine-131 in $1.0\text{ kg}$ of water must be below $170\text{ Bq}$. Calculate the time, in days, for the activity of the contaminated water in (b) to fall to $170\text{ Bq}$.