Answer:
B
Step-by-step explanation:
This is due to the differences in the concentrations of the radioactive isotopes in the two containers of the same volume. In container A, with a higher density of atoms, there is a higher chance of a neutron released in the decay of one atom, hitting another atom and splitting it. This is in comparison to container B that has fewer atoms that are widely dispersed due to the lower density. Atoms in cointainer A will therefore decay faster (shorter half-life) than atoms in container B.