The distillation column shown in the drawing is used to distill a binary mixture. symbols x, y, and z denote mole frac- tions of the more volatile component, while b, d, r, and f represent molar flow rates. it is desired to control distillate composition y despite disturbances in feed flow rate f. all flow rates can be measured and manipulated with the excep- tion of f, which can only be measured. a composition ana- lyzer provides measurements of y.

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6

a chemical change results in a new substance being formed; whereas a physical change will result in a different state of matter

explanation: