Final answer:
The correct salt that could have been added to the sulfuric acid solution to cause the light bulb to dim is Barium nitrate (Ba(NO3)2). It forms a precipitate of barium sulfate, which is only slightly soluble, reducing the conductivity of the solution.
Step-by-step explanation:
When the exposed electrodes of a light bulb are placed in a solution and upon adding a dilute salt solution the bulb dims, it indicates that the conductivity of the solution has decreased. The addition of Barium nitrate (Ba(NO3)2) would cause such an effect because the sulfate ions (SO42-) from sulfuric acid (H2SO4) react with barium ions (Ba2+) to form barium sulfate (BaSO4), a white precipitate that is only slightly soluble in water. This decreases the number of free ions available to conduct electricity. The balanced chemical equation for the precipitation that occurs when Ba(NO3)2 is added to a solution of H2SO4 is as follows:
Ba(NO3)2(aq) + H2SO4(aq) → BaSO4(s) + 2HNO3(aq)
Therefore, the correct salt that could have been added to dim the light bulb in the solution of H2SO4 is Ba(NO3)2 (option a). The formation of BaSO4 reduces the overall conductivity of the solution, leading to the observed dimming of the bulb.