Please i need help with this question. Please show workings where necessary and proof/ explain your point​

Significant figures are digits read directly from the measuring instrument plus one more digit, which is __ by the observer.

Briefly explain the process of refining of petroleum.

What does hund's rule state? a. an orbital can contain two electrons only if the electrons have opposite spins. b. an orbital can contain two electrons only if all other orbitals at that sublevel are empty. c. an orbital can contain two electrons only if the electrons have different energy levels. d. an orbital can contain two electrons only if all other orbitals in that sublevel contain at least one electron.