Me

it is not possible to separate by physical means.

a)mixtures
b)salt water
c)solutions
d)compounds

I'm pretty sure it's D. Compounds
Salt water is an example of a solution, and a solution is a type of mixture, so by multiple choice logic none can be the right answer! Seriously though - mixture are combinations of two compounds that are physically combined but do not undergo a chemical reaction with one another to produce a new compound. For instance, when you dissolve salt in water, you don't produce any new products, and you can boil away the water to leave only the salt (a physical method of separation). You cannot separate a compound by physical means because by definition this would be a chemical reaction as you're breaking bonds.

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

D-no effect on the rate