Need answer asap ! which of these elements has four valence electrons? (a). hafnium (hf) (b.) radon (rn) (c.) silicon (si) (d.) sulfur (s)

Select for each of the following statements whether it is correct or incorrect. (a) in an isothermal expansion of an ideal gas. (b) the temperature remains constant. (b) the pressure remains constant. (c) there is work done by the gas. (d) there is heat added to the gas. (e) the change in internal energy equals zero.