A143.1 g sample of a compound contains 53.4 g of carbon, 16.9 g of hydrogen, 43 g of nitrogen, and some amount of oxygen. what is the mass percent of oxygen in the compound?

Mass of oxygen = 143,1g - (53,4g + 16,9g + 43g) = 29,8g

If 143,1g is 100%
                       so
   29,8g   is %O

%O = (29,8g*100%) / 143,1g = 20,82%

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

Answer) by studying proton collisions hope this : )