4.The other light bulb will stay on and glow brightly.
The main difference between the 3 isotopes of hydrogen are the number of neutrons in the nucleus. Hydrogen has no neutrons, Deuterium has one neutron, and tritium has two neutrons. All three have one proton and one electron.
A solution is turning blue means, it is turning it's behavior to Basic from Acidic. Reagent D must be a Basic component so it is increasing the pH of the solution. As reaction does not depend on the phase of the component, it could be anything i.e., Solid, Liquid or gas.
Hope this helps!
