How could you use a thin glass tube to place the crystal at the bottom of the beaker of water​

Aquantity of that isotope to decay to 1/2 of  its original value

The answer this would be radiative zone

In reversible reaction chemistry equilibrium is attained when the forward and reverse reactions are taking place at the same rate, thus, the concentrations of reactants and products remain the same. a reversible reaction is a chemical reaction where the reactants form products that, in turn, react together to give the reactants back. in irreversible reactions on the other hand, the reactants react to form the products, which cannot revert back into reactants.