Which pair of metals produces the highest voltage and why

The maximum voltage can be produced in the cell which have higher difference in the electrocemical potential , in this case it would be most reactive magnesium and less reactive platinum...magnesum spontaneously gives its two electron and Pt takes its two electron.... as result generates the highest voltage

Dmight be the correct answer

The  grandmother cell  is a hypothetical  neuronthat represents a complex but specific concept or object.[1]  it activates when a person "sees, hears, or otherwise sensibly discriminates"[2]  a specific entity, such as his or her grandmother. the term was in use at least as early as 1966 amongst staff and students in the department of experimental psychology, university of cambridge, england. a similar concept, that of the  gnostic neuron, was proposed two years later