Isotopes of the same element differ only in the number of neutrons an atom has. Its still the same element because the number of protons define an element. Just their neutrons and mass number is different.
Greater rainfall has an greater increase on the rate of chemical weathering. Rain is a form of precipitation.
Answer : The 
must be administered.
Solution :
As we are given that a vial containing radioactive selenium-75 has an activity of 
.
As, 3.0 mCi radioactive selenium-75 present in 1 ml
So, 2.6 mCi radioactive selenium-75 present in 
Conversion :
Therefore, the must be administered.
Ca + Cl2 ->CaCl2 <span>synthesis (check your chemistry lesson)</span>
