What must be true for a spontaneous reaction in an electrochemical cell? the overall cell potential must be positive. the overall cell potential must be negative. the cathode’s standard reduction potential must be positive. the cathode’s standard reduction potential must be negative.

It is the overall cell potential what tells if a reacton in an electrochemical cell is spontaneous.

This is, the net cell potential, which is calculated as the difference Reduction Standard Potential less Oxidation Standard Potential, is what accounts to determine whether the reaction is spontaeous or  not. 

When the net cell potential is positive the redox reaction is spontaneous.

So, the answer is the first statement; "The overall cell potential must be positive".

Yes, endothermic means it turns cold. and some chemical changes include change of tempature.