1.. the region in which an electron is most likely to be found is called a(an)
2. an atom in which an electron has moved to a higher energy level is in a(an) state.
3. when mendeleev organized elements in his periodic table in order of increasing mass, elements with similar properties were in the same
4. mendeleev’s periodic table was useful because it enabled scientists to predict properties of unknown

1. The region in which an electron is most likely to be found is called an orbital.

2. An atom in which an electron has moved to a higher energy level is in an excited state.

3. When Mendeleev organized elements in his periodic table in order of increasing mass, elements with similar properties were in the same column. 

4. Mendeleev’s periodic table was useful because it enabled scientists to predict properties of unknown elements.

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