How can the melting and boiling point be used to determine the state of an element at room temperature?

Room temp is usualy 25 degree celcius if the mealting point is lower than 25 than is liquid if the boiling point is also lower than 25 than it is  in vapour form if visa-versa than it is solid form

The activity series is shown in the attached picture. if the element is below the other, then you can displace the other. following the activity series as a guide, the reactions are as follows: nickel and aluminum chloride3 ni + 2 alcl₃  → 3 nicl₂ + 2 albarium and copper bromideba + cubr  →  no reaction because cu is less oxidizable than bapotassium nitrate and aluminum3 kno₃ + al  → al(no₃)₃ + 3 ksodium phosphate and zincnaso₄ + zn  → znso₄ + na