all positive electrodes are anodes and all negative electrodes are cathodes is it true or false

The statement is generally true in most contexts, but not always. In a galvanic (voltaic) cell, which is a type of electrochemical cell that uses spontaneous redox reactions to generate electricity, the anode is the electrode where oxidation (loss of electrons) occurs, and it is negative. The cathode is the electrode where reduction (gain of electrons) occurs, and it is positive.

However, in an electrolytic cell, which uses electrical energy to drive a non-spontaneous redox reaction, the anode is the electrode where oxidation occurs, and it is positive. The cathode is the electrode where reduction occurs, and it is negative.

So, while it's common to associate anodes with positivity and cathodes with negativity, the truth is that whether an electrode is an anode or a cathode is determined by the direction of the flow of electrons, not by its charge. Therefore, the statement "all positive electrodes are anodes and all negative electrodes are cathodes" is not always true.