The difference between $$\Delta \mathrm{H}$$ and $$\Delta \mathrm{U}$$ is usually significant for systems consisting of :

Which of the following elements is doped with to obtain fibre amplifiers for optical fibre communication system?

What is the half life of a first order reaction if rate constant is $$4.2 \times 10^{-2}$$ per day?

What type of solution is the ethyl alcohol in water?