Define a standard.

Which defines the standard reduction electrode potential of Zn^(2+) ions :

In defining the standard of length we have to specify the temperature at which measurement should be made. Are we justified in calling length a fundamental quantity if another physical quantity, temperature has to be specified in choosing a standard?

Which is not true for a standard hydrogen electrode :

What is the difference between unit and standard.

What is the emf of a standard hydrogen electrode?

What is the advantage in choosing the wavelength of a light radiation as a standard of length?

Define BOD