(a(i))[2]
State what the term radioactive means.
(a(ii))[2]
State what is meant by the decay constant.
(b)[2]
Water has become contaminated with iodine-131. The activity of the iodine-131 in $1.0\,\text{kg}$ of water is $560\,\text{Bq}$. Determine how many iodine-131 atoms are present in $1.0\,\text{kg}$ of water.
(c)[3]
Regulations state 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 $170\,\text{Bq}$.