Answer:
(D.)
The core of the pyruvate dehydrogenase complex is made up of eight catalytic <u>trimers </u>that make up the<u> E2</u> component.
Explanation:
Eight trimers assemble as a hollow truncated cube, which forms the core of the multi-enzyme complex, known as the E2 complex in human pyruvate dehydrogenase complex.
9 g of hydrogen - 42 g of nitrogen
5 g of hydrogen - x g of nitrogen

The mass of nitrogen in the second sample is 23.33 g.
Answer:
All atoms of the same element have always have the same amount of protons.
Explanation:
Atoms of the same element have always have the same amount of protons but not always the same electrons and neutrons. If an atom gains or loses one of its valance electrons, the electrons on the outermost shell, then it becomes ionized. Also not all atoms of the same element have the same amount of neutron. This is called an isotope. A good example would be Carbon 13. Normally, Carbon atoms have an atomic mass of 12 AMU or 12 atomic mass units. However, Carbon atoms have an atomic mass of 13 AMU, consisting of 7 neutrons instead of 6 neutrons. So the only thing that all atoms of the same element have in common is the amount of protons.