The bulb glows in the presence of acids during the activity because acids promote the flow of electric current, completing the circuit and allowing the bulb to light up. Acids contain ions, such as hydrogen ions (H⁺), which can conduct electricity when dissolved in water. When the electrodes are immersed in an acidic solution, the ions facilitate the flow of electrons between them, creating an electric current. This current passes through the filament of the bulb, heating it and causing it to emit light. The ability of acids to conduct electricity is a fundamental property related to their ionization in aqueous solutions.