Carbonate mgco3, reacts with nitric acid, hno3, to form magnesium nitrate and carbonic acid. carbonic acid reacts to form water and carbon dioxide. which type of reaction does carbonic acid undergo ?

Most likely the carbonic acid im guessing H2CO3 undergoes thermal decomposition 

H2CO3 ===> H2O + CO2

hope that helps

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