B

Step 1: Understanding thermocouples involves knowing that they are made of two different metals which produce a voltage (thermo e.m.f.) when subjected to a temperature difference, based on the Seebeck effect.
Step 2: Above neutral temperature, as temperature increases, the difference in how the two metals respond to heat typically leads to an increase in the generated thermo e.m.f.
Step 3: This is due to the enhanced mobility of charge carriers at higher temperatures, which usually yields a greater potential difference.
Conclusion: Therefore, the correct option is that the thermo e.m.f. increases with rise in temperature.