Fuel cell, using hydrogen and oxygen as fuels,

A. has been used in spaceship

B. has as efficiency of $$40 \%$$ to produce electricity

C. uses aluminum as catalysts

D. is eco-friendly

E. is actually a type of Galvanic cell only

Choose the correct answer from the options given below:

For a strong electrolyte, a plot of molar conductivity against (concentration) $${ }^{1 / 2}$$ is a straight line, with a negative slope, the correct unit for the slope is

One of the commonly used electrode is calomel electrode. Under which of the following categories, calomel electrode comes?

What pressure (bar) of $$\mathrm{H}_2$$ would be required to make emf of hydrogen electrode zero in pure water at $$25^{\circ} \mathrm{C}$$ ?